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 A117961 Hexagonal numbers with prime indices. 3
 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; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 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. LINKS FORMULA 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)). MATHEMATICA With[{hex=Table[n(2n-1), {n, 250}]}, Flatten[Table[Take[hex, {Prime[n]}], {n, 40}]]] (* Harvey P. Dale, Dec 04 2011 *) CROSSREFS Cf. A000005, A000040, A000384, A001021, A034953, A001248, A116995. Sequence in context: A193449 A197160 A182420 * A327769 A318482 A095122 Adjacent sequences:  A117958 A117959 A117960 * A117962 A117963 A117964 KEYWORD easy,nonn,less AUTHOR Jonathan Vos Post, Apr 05 2006 STATUS approved

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Last modified May 18 11:30 EDT 2021. Contains 343995 sequences. (Running on oeis4.)