A190052 Least number having exactly two odd prime factors that differ by 2*n^2.

15, 33, 115, 185, 159, 553, 303, 393, 835, 2321, 7859, 1465, 3839, 1985, 3199, 5753, 13823, 3265, 3635, 8921, 4435, 2913, 3183, 12793, 37091, 40049, 19123, 4713, 18623, 19921, 21263, 10265, 64003, 67889, 41939, 44353, 8223, 84593, 21343, 9609, 37103, 17665

Offset

1,1

Links

Nathaniel Johnston, Table of n, a(n) for n = 1..10000

Example

a(11) = 7859 because 7859 = 29 * 271, and 271 - 29 = 242 = 2*11^2.

Maple

A190052 := proc(n) local k, p: k:=1: do p:=ithprime(k): if(isprime(p+2*n^2))then return p*(p+2*n^2): fi: k:=k+1: od: end: seq(A190052(n), n=1..50); # Nathaniel Johnston, May 04 2011

Mathematica

f[n_] := Block[{p = 3}, While[q=p+2*n^2; ! PrimeQ[q], p=NextPrime[p]]; p*q]; Table[ f[n], {n, 60}]

Crossrefs

Sequence in context: A211327 A222179 A322493 * A242243 A219855 A270072

Adjacent sequences: A190049 A190050 A190051 * A190053 A190054 A190055

Keyword

nonn,easy

Author

Michel Lagneau, May 04 2011

Status

approved