A005521 1 + (sum of first n odd primes - n)/2.

1, 2, 4, 7, 12, 18, 26, 35, 46, 60, 75, 93, 113, 134, 157, 183, 212, 242, 275, 310, 346, 385, 426, 470, 518, 568, 619, 672, 726, 782, 845, 910, 978, 1047, 1121, 1196, 1274, 1355, 1438, 1524, 1613, 1703, 1798

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Crossrefs

a(n+1) - 1 counts primorial intervals A065917.

Partial sums of A005521.

Formula

a(n+1) = a(n) + (prime(n+1) - 1)/2 for odd primes prime(n+1).

a(n+2) - 2*a(n+1) + a(n) = A028334(n). - Frank Ellermann