A219603 a(n) = prime(n) * prime(2*n-1).

4, 15, 55, 119, 253, 403, 697, 893, 1357, 1943, 2263, 3071, 3977, 4429, 5123, 6731, 8083, 9089, 10519, 11857, 13067, 15089, 16351, 18779, 22019, 23533, 24823, 27499, 29321, 31301, 35941, 40217, 42881, 46009, 51703, 53303, 57619, 61777, 64963, 69373, 75001

Offset: 1

Author

Reinhard Zumkeller, Nov 25 2012

Keywords

• nonn

Comments

A020639(a(n)) = A000040(n); A006530(a(n)) = A031368(n);

a(n) is central term of row 2n-1 of semiprimes triangle (A087112).

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Subsequence of A001358.

Cf. A006094.

Programs

Haskell

a219603 n = a000040 n * a031368 n

PARI

a(n)=prime(n) * prime(2*n-1) \\ Charles R Greathouse IV, Feb 07 2017

Formula

a(n) = A000040(n) * A031368(n).