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Search: id:A123176
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| A123176 |
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Numbers n such that (2^p + 1)/3 is prime, where p is the n-th prime. |
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2
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| 2, 3, 4, 5, 6, 7, 8, 9, 11, 14, 18, 22, 26, 31, 39, 43, 46, 65, 69, 126, 267, 380, 495, 762, 1285, 1304, 1364, 1479, 1697, 4469, 8135, 9193, 11065, 11902, 12923, 13103, 23396, 23642, 31850
(list; graph; listen)
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OFFSET
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1,1
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LINKS
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C. Caldwell's The Top Twenty, Wagstaff.
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FORMULA
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a(n) = PrimePi( A000978(n) ).
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CROSSREFS
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Cf. A000978, A000979, A001045, A049883, A107036.
Wagstaff primes or primes of form (2^p + 1)/3 are listed in A000979(n) = {3,11,43,683,2731,43691,174763,2796203,715827883,...}.
Numbers n such that (2^n + 1)/3 is prime are listed in A000978(n) = Prime(a(n)) = {3,5,7,11,13,17,19,23,31,43,61,79,101,127,167,191,...}.
Also prime(n) are the indices of prime Jacobsthal numbers (A001045) with prime indices. Primes in the Jacobsthal sequence are listed in A049883(n) = {3,5,11,43,683,2731,43691,174763,...}.
Indices of prime Jacobsthal numbers are listed in A107036(n) = {3,4,5,7,11,13,17,19,23,31,43,61,79,...}, where A107036(1) = 4 is the only composite index of prime Jacobsthal number.
Sequence in context: A085429 A082324 A079064 this_sequence A017902 A005710 A023358
Adjacent sequences: A123173 A123174 A123175 this_sequence A123177 A123178 A123179
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KEYWORD
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more,nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 03 2006
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