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Search: id:A116995
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| A116995 |
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Pentagonal numbers with prime indices. |
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+0
4
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| 5, 12, 35, 70, 176, 247, 425, 532, 782, 1247, 1426, 2035, 2501, 2752, 3290, 4187, 5192, 5551, 6700, 7526, 7957, 9322, 10292, 11837, 14065, 15251, 15862, 17120, 17767, 19097, 24130, 25676, 28085, 28912, 33227, 34126, 36895, 39772, 41750, 44807
(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: A001248 Squares of primes. A034953 Triangular numbers (A000217) with prime indices.
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FORMULA
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a(n) = Prime(n)*(3*Prime(n)-1)/2. a(n) = A000326(A000040(n)).
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EXAMPLE
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a(1) = Pentagonal(prime(1)) = A000326(2) = 2*(3*2-1)/2 = 5.
a(2) = Pentagonal(prime(2)) = A000326(3) = 3*(3*3-1)/2 = 12.
a(3) = Pentagonal(prime(3)) = A000326(5) = 5*(3*5-1)/2 = 35.
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MATHEMATICA
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Table[Prime[n]*(3*Prime[n] - 1)/2, {n, 1, 60}] - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Apr 04 2006
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CROSSREFS
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Cf. A000040, A000326, A001248, A034953.
Sequence in context: A066280 A136113 A050189 this_sequence A032281 A077918 A034752
Adjacent sequences: A116992 A116993 A116994 this_sequence A116996 A116997 A116998
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost2(AT)yahoo.com), Apr 02 2006
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