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A083221
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Sieve of Eratosthenes arranged as an array and read by antidiagonals as A(1,1), A(1,2), A(2,1), A(1,3), A(2,2), A(3,1), ...
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85
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2, 4, 3, 6, 9, 5, 8, 15, 25, 7, 10, 21, 35, 49, 11, 12, 27, 55, 77, 121, 13, 14, 33, 65, 91, 143, 169, 17, 16, 39, 85, 119, 187, 221, 289, 19, 18, 45, 95, 133, 209, 247, 323, 361, 23, 20, 51, 115, 161, 253, 299, 391, 437, 529, 29, 22, 57, 125, 203, 319, 377, 493, 551, 667
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OFFSET
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2,1
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COMMENTS
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This is permutation of natural numbers larger than 1.
If we assume here that a(1) = 1 (but which is not explicitly included because outside of the array), then A252460 gives an inverse permutation. See also A249741.
For navigating in this array:
A055396(n) gives the row number of row where n occurs, and A078898(n) gives its column number, both starting their indexing from 1.
A250469(n) gives the number immediately below n, and when n is an odd number >= 3, A250470(n) gives the number immediately above n. If n is a composite, A249744(n) gives the number immediately left of n.
First cube of each row, which is {the initial prime of the row}^3 and also the first number neither a prime or semiprime, occurs on row n at position A250474(n).
(End)
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LINKS
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EXAMPLE
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The top left corner of the array:
2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26
3, 9, 15, 21, 27, 33, 39, 45, 51, 57, 63, 69, 75
5, 25, 35, 55, 65, 85, 95, 115, 125, 145, 155, 175, 185
7, 49, 77, 91, 119, 133, 161, 203, 217, 259, 287, 301, 329
11, 121, 143, 187, 209, 253, 319, 341, 407, 451, 473, 517, 583
13, 169, 221, 247, 299, 377, 403, 481, 533, 559, 611, 689, 767
17, 289, 323, 391, 493, 527, 629, 697, 731, 799, 901, 1003, 1037
19, 361, 437, 551, 589, 703, 779, 817, 893, 1007, 1121, 1159, 1273
23, 529, 667, 713, 851, 943, 989, 1081, 1219, 1357, 1403, 1541, 1633
29, 841, 899, 1073, 1189, 1247, 1363, 1537, 1711, 1769, 1943, 2059, 2117
...
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MATHEMATICA
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lim = 11; a = Table[Take[Prime[n] Select[Range[lim^2], GCD[# Prime@ n, Product[Prime@ i, {i, 1, n - 1}]] == 1 &], lim], {n, lim}]; Flatten[Table[a[[i, n - i + 1]], {n, lim}, {i, n}]] (* Michael De Vlieger, Jan 04 2016, after Yasutoshi Kohmoto at A083140 *)
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PROG
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(define (A083221 n) (if (<= n 1) n (A083221bi (A002260 (- n 1)) (A004736 (- n 1))))) ;; Gives 1 for 1 and then the terms of this square array: (A083221 2) = 2, (A083221 3) = 4, etc.
(define (A083221bi row col) ((rowfun_n_for_A083221 row) col))
(definec (rowfun_n_for_A083221 n) (if (= 1 n) (lambda (n) (+ n n)) (let ((rowfun_of_Esieve (rowfun_n_for_Esieve n)) (prime (A000040 n))) (COMPOSE rowfun_of_Esieve (MATCHING-POS 1 1 (lambda (i) (zero? (modulo (rowfun_of_Esieve i) prime))))))))
(definec (A000040 n) ((rowfun_n_for_Esieve n) 1))
(definec (rowfun_n_for_Esieve n) (if (= 1 n) (lambda (n) (+ 1 n)) (let* ((prevrowfun (rowfun_n_for_Esieve (- n 1))) (prevprime (prevrowfun 1))) (COMPOSE prevrowfun (NONZERO-POS 1 1 (lambda (i) (modulo (prevrowfun i) prevprime)))))))
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CROSSREFS
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Cf. A002260, A004736, A004280, A020639, A038179, A055396, A078898, A138511, A249820, A249730, A249735, A249744, A250469, A250470, A250472, A250474.
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KEYWORD
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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