A049880 a(n) is the number of distinct sums of 2 different primes chosen from the first n primes.

1, 3, 6, 10, 13, 17, 21, 25, 29, 35, 39, 45, 50, 54, 59, 63, 70, 75, 81, 86, 91, 97, 102, 109, 114, 119, 125, 130, 135, 143, 148, 154, 162, 168, 175, 181, 187, 195, 200, 206, 213, 218, 224, 230, 236, 242, 249, 258, 263

Offset

2,2

Comments

That is, number of numbers of the form prime(i) + prime(j) with 1 <= i < j <= n, where prime(k) = k-th prime. - N. J. A. Sloane, Jun 05 2015

Links

Zak Seidov, Table of n, a(n) for n = 2..1000

Example

For n = 5, the sums are 5, 7, 8, 9, 10, 12, 13, 14, 16, 18. - N. J. A. Sloane, Jun 05 2015

Prog

(PARI) a(n)={my(pr=primes(n), sums=Set()); for(i=1, n-1, for(j=i+1, n, s=pr[i]+pr[j]; sums=setunion(sums, Set(s))); ); length(sums); } \\ Michel Marcus, Oct 02 2013

Crossrefs

Cf. A000040, A049881, A049882, A253250 (first differences).

Sequence in context: A310056 A189524 A288205 * A276219 A267593 A248221

Adjacent sequences: A049877 A049878 A049879 * A049881 A049882 A049883

Keyword

nonn

Author

Clark Kimberling

Extensions

Name edited by Petros Hadjicostas, Nov 19 2019

Status

approved