A111350 - OEIS

%I #15 Jan 26 2023 12:30:41

%S 4,16,25,64,100,144,169,196,225,289,324,361,529,784,961,1024,1521,

%T 1936,2304,2401,2500,2809,2916,3025,3249,3364,3600,3969,4096,4624,

%U 4761,5041,5776,6084,6561,6724,7056,7225,7396,7921,8100,8281,10816,11664,12321

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

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

%t Select[Range[111]^2, Plus @@ Last /@ FactorInteger[2# + 1] == 2 &] (* _Ray Chandler_, Nov 10 2005 *)

%t Select[Range[120]^2,PrimeOmega[2#+1]==2&] (* _Harvey P. Dale_, Jul 22 2013 *)

%Y Cf. A111351, A112777.

%K nonn

%O 1,1

%A _Giovanni Teofilatto_, Oct 29 2005

%E Edited and extended by _Ray Chandler_, Nov 10 2005

%E Offset corrected by _Arkadiusz Wesolowski_, Aug 09 2011