A084410 First column of triangle A084408.

1, 2, 5, 4, 13, 10, 31, 20, 30, 42, 61, 55, 109, 70, 88, 108, 181, 126, 277, 148, 174, 201, 397, 225, 255, 287, 318, 348, 547, 382, 733, 417, 456, 496, 535, 576, 947, 621, 666, 711, 1213, 758, 1499, 805, 858, 910, 1831, 963, 1020, 1078, 1137, 1195, 2207, 1255

Offset: 1

Author

Amarnath Murthy, Jun 01 2003

Keywords

• nonn
• easy

Comments

a(n) is prime iff n is prime.

Crossrefs

Cf. A084408, A084409, A084411.

Formula

For n prime, a(n) = p(A034387(n)-n+1). For n composite, a(n) = A002808([n*(n+1)/2]-A034387(n)-n).

Extensions

Edited and extended by David Wasserman, Dec 27 2004