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Search: id:A117961
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| A117961 |
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Hexagonal numbers with prime indices. |
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+0
2
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| 6, 15, 45, 91, 231, 325, 561, 703, 1035, 1653, 1891, 2701, 3321, 3655, 4371, 5565, 6903, 7381, 8911, 10011, 10585, 12403, 13695, 15753, 18721, 20301, 21115, 22791, 23653, 25425, 32131, 34191, 37401, 38503, 44253, 45451, 49141, 52975, 55611
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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See also: A034953 Triangular numbers (A000217) with prime indices. A001248 Squares of primes. A116995 Pentagonal numbers with prime indices. A000384 Hexagonal numbers: n(2n-1). There are no prime hexagonal numbers. The n-th Hexagonal number A000384(n) = n*(2*n-1) is semiprime iff both n and 2*n-1 are prime iff A000384(n) is an element of A001358 iff n is an element of A005382.
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FORMULA
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a(n) = A000040(n)*(2*A000040(n)-1). a(n) = A000384(prime(n)). a(n) = number of divisors of 12^(prime(n)-1) = A000005(A001021(A000040(n)-1)).
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CROSSREFS
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Cf. A000005, A000040, A000384, A001021, A034953, A001248, A116995.
Sequence in context: A114696 A106368 A100491 this_sequence A095122 A082637 A106272
Adjacent sequences: A117958 A117959 A117960 this_sequence A117962 A117963 A117964
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KEYWORD
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easy,nonn,less
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Apr 05 2006
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