A114970 - OEIS

%I #32 Jan 01 2025 18:27:55

%S 5,7,17,25,43,61,69,73,105,111,117,123,135,141,171,219,231,241,309,

%T 321,543,739,795,833,975

%N Numbers m such that 2^m + m^2 is a semiprime.

%C a(26) >= 1125. - _Tyler Busby_, Dec 27 2024

%H factordb.com, <a href="http://factordb.com/index.php?query=2%5E1125%2B1125%5E2">Status of 2^1125+1125^2</a>.

%e 2^5 + 5^2 = 32 + 25 = 57 = 3*19 (semiprime).

%t Select[Range[200], PrimeOmega[2^# + #^2]==2&] (* _Vincenzo Librandi_, May 21 2014 *)

%o (Magma)IsSemiprime:=func< n | &+[ k[2]: k in Factorization(n) ] eq 2 >; [ n: n in [1..175]|IsSemiprime(2^n+n^2)]; // _Vincenzo Librandi_, Dec 16 2010

%Y Cf. A114971, A114973, A114974.

%K nonn,more,hard

%O 1,1

%A _Zak Seidov_, Feb 22 2006

%E a(16)-a(21) from _Luke March_, Jul 27 2015

%E a(22) from _Hugo Pfoertner_, Jul 28 2019

%E a(23)-a(25) from _Tyler Busby_, Dec 27 2024