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A293715
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Numbers k such that A007755(k) is prime.
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0
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2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 16, 18, 19, 21, 23, 24, 27, 28, 31, 33, 43, 51, 53, 54, 57, 60, 61, 62, 65, 67, 68, 69, 71, 73, 76, 79, 81, 83, 84, 89, 91, 110, 111, 115, 116, 118, 121, 124, 126, 129, 131, 132, 138, 139, 144, 145, 147, 149, 150, 153, 156
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OFFSET
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1,1
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COMMENTS
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Shapiro conjectured that A007755(n) is prime for all n > 1, and verified it up to n = 10. Mills showed that A007755(34)=(2^16+1)^2 is composite.
The least number n such that Omega(A007755(n)) = 1, 2, 3, ... is 2, 13, 30, 58, 74, 90, 106, 122, 146, 162, 178, 194, 210, 226, ... (Omega is the number of prime factors with multiplicity, A001222).
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REFERENCES
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Richard K. Guy, Unsolved Problems in Number Theory, 3rd Edition, Springer, 2004, B41, p. 148.
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LINKS
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EXAMPLE
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The first 11 values of A007755(n) after n=1 are the primes: 2, 3, 5, 11, 17, 41, 83, 137, 257, 641, 1097, 2329, therefore 2-12 are in the sequence.
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MATHEMATICA
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s = Import[b007755.txt", "Data"][[All, 2]]; a = Flatten[Position[s, _?(PrimeQ[#] &)]] (* using the b-File from A007755 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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