A108769 - OEIS

%I #13 Nov 17 2022 08:14:19

%S 3,6,8,10,11,13,15,16,18,20,26,27,31,33,37,38,40,43,44,45,48,51,52,54,

%T 55,56,57,59,62,63,64,67,68,73,74,75,76,77,80,81,83,89,92,94,98,105,

%U 107,111,112,113,114,117,120,123,124,129,131,133,134,138,140,141,142,143

%N Numbers m such that m^2 + (m+1)^2 is a semiprime.

%C Numbers m such that A099776(m) is a semiprime. - _Michel Marcus_, Nov 17 2022

%H Alois P. Heinz, <a href="/A108769/b108769.txt">Table of n, a(n) for n = 1..65536</a>

%p a:= proc(n) local k; for k from 1+`if`(n=1, 0, a(n-1))

%p       while (t-> isprime(t) or numtheory[bigomega](t)

%p       >2)(2*k*(k+1)+1) do od: k

%p     end:

%p seq(a(n), n=1..70);  # _Alois P. Heinz_, Aug 01 2019

%t Select[Range[1000], PrimeOmega[#^2 + (#+1)^2] == 2&] (* _Jean-François Alcover_, Nov 17 2022 *)

%o (PARI) isok(m) = bigomega(m^2 + (m+1)^2) == 2; \\ _Michel Marcus_, Nov 17 2022

%Y Cf. A001358, A027861, A099776.

%K easy,nonn

%O 1,1

%A _Jason Earls_, Jun 25 2005