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

Author

Jonathan Vos Post, Apr 02 2006

Keywords

• easy
• nonn

Comments

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

Examples

			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.
		

Crossrefs

Cf. A000040, A000326, A001248, A034953.

Programs

Mathematica

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

Formula

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