A024850 Let c(k) denote the k-th composite number and p(k) the k-th prime number; then a(n) = Sum_{i=n*(n-1)/2+1 .. n*(n+1)/2} c(i) - Sum_{i=1..n} p(i).

2, 9, 21, 46, 84, 135, 206, 308, 429, 583, 772, 987, 1265, 1552, 1906, 2308, 2767, 3278, 3840, 4478, 5201, 5956, 6783, 7704, 8706, 9777, 10976, 12241, 13591, 14985, 16546, 18230, 20019, 21862, 23824, 25907, 28111, 30474, 32897, 35482, 38208, 41125, 44159, 47239, 50516, 53944

Offset

1,1

Links

Table of n, a(n) for n=1..46.

Formula

a(n) = A072475(n) - A007504(n) [corrected by Sean A. Irvine, Jul 26 2019].

Example

a(1) = 4 - 2 = 2.
a(2) = 6 + 8 - 2 - 3 = 9.
a(3) = 9 + 10 + 12 - 2 - 3 - 5 = 21.

Crossrefs

Cf. A071411.

Sequence in context: A131476 A023549 A192971 * A237044 A342713 A248116

Adjacent sequences: A024847 A024848 A024849 * A024851 A024852 A024853

Keyword

nonn

Author

Amarnath Murthy and Benoit Cloitre, Jun 23 2002

Extensions

a(7) and a(8) corrected and more terms from Sean A. Irvine, Jul 26 2019

Status

approved