A111350 Squares n such that 2*n + 1 is a semiprime.

4, 16, 25, 64, 100, 144, 169, 196, 225, 289, 324, 361, 529, 784, 961, 1024, 1521, 1936, 2304, 2401, 2500, 2809, 2916, 3025, 3249, 3364, 3600, 3969, 4096, 4624, 4761, 5041, 5776, 6084, 6561, 6724, 7056, 7225, 7396, 7921, 8100, 8281, 10816, 11664, 12321

Offset

1,1

Links

Table of n, a(n) for n=1..45.

Formula

a(n) = (A111351(n)-1)/2 = A112777(n)^2.

Mathematica

Select[Range[111]^2, Plus @@ Last /@ FactorInteger[2# + 1] == 2 &] (* Ray Chandler, Nov 10 2005 *)
Select[Range[120]^2, PrimeOmega[2#+1]==2&] (* Harvey P. Dale, Jul 22 2013 *)

Crossrefs

Cf. A111351, A112777.

Sequence in context: A295921 A338406 A351979 * A223221 A210002 A105078

Adjacent sequences: A111347 A111348 A111349 * A111351 A111352 A111353

Keyword

nonn

Author

Giovanni Teofilatto, Oct 29 2005

Extensions

Edited and extended by Ray Chandler, Nov 10 2005

Offset corrected by Arkadiusz Wesolowski, Aug 09 2011

Status

approved