A116995 Pentagonal numbers with prime indices.

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

Offset

1,1

Comments

See also: A001248 Squares of primes. A034953 Triangular numbers (A000217) with prime indices.

Links

Table of n, a(n) for n=1..40.

Formula

a(n) = Prime(n)*(3*Prime(n)-1)/2. a(n) = A000326(A000040(n)).

Example

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.

Mathematica

Table[Prime[n]*(3*Prime[n] - 1)/2, {n, 1, 60}] (* Stefan Steinerberger, Apr 04 2006 *)

Crossrefs

Cf. A000040, A000326, A001248, A034953.

Sequence in context: A298992 A050189 A308344 * A032281 A294654 A229043

Adjacent sequences: A116992 A116993 A116994 * A116996 A116997 A116998

Keyword

easy,nonn

Author

Jonathan Vos Post, Apr 02 2006

Status

approved