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A057061
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a(n) = number of the column of (R(i,j)) that contains prime(n), where R(i,j) is the rectangle with antidiagonals 1; 2,3; 4,5,6; ...
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2
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2, 1, 2, 4, 5, 3, 5, 3, 6, 8, 6, 9, 5, 3, 9, 3, 8, 6, 12, 8, 6, 13, 9, 3, 9, 5, 3, 14, 12, 8, 10, 6, 17, 15, 5, 3, 15, 9, 5, 18, 12, 10, 20, 18, 14, 12, 21, 9, 5, 3, 21, 15, 13, 3, 20, 14, 8, 6, 24, 20, 18, 8, 19, 15, 13, 9, 21, 15, 5, 3, 26, 20, 12, 6
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OFFSET
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1,1
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COMMENTS
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The rectangle R(i,j) has this corner:
1, 2, 4, 7, 11, 16, 22, 29, ...
3, 5, 8, 12, 17, 23, 30, 38, ...
6, 9, 13, 18, 24, 31, 39, 48, ...
10, 14, 19, 25, 32, 40, 49, 59, ...
15, 20, 26, 33, 41, 50, 60, 71, ...
21, 27, 34, 42, 51, 61, 72, 84, ...
28, 35, 43, 52, 62, 73, 85, 98, ...
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LINKS
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FORMULA
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EXAMPLE
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The 8th prime, 19, is in column 3, so a(8) = 3.
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PROG
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(PARI) f(n) = 1 + binomial(1 + floor(1/2 + sqrt(2*n)), 2) - n; \\ A004736
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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