A140667 - OEIS

%I #8 Jan 31 2023 11:53:43

%S 91,1581,2465,8481,25761,31609,33355,34945,118405,146611,319507,

%T 736291,994507,3270403,3375487,5176153,6186403,6228685,8650951,

%U 10679131,22028203,26017291,31470211,33796531,41710411,42149971,42474547,46672291,48316969,49019851,58986091,68182003,69885649

%N Odd composite numbers k for which k = A140607((k-1)/2).

%o (PARI) f(n) = (eulerphi(2*n+1) + 1 + g(n))/2; \\ A140607

%o g(n) = sumdiv(2*n+1, d, eulerphi(d)/(t=znorder(Mod(2, d))))*t-t+1; \\ A137576

%o isok(c) = if (!isprime(c) && (c%2), f((c-1)/2) == c); \\ _Michel Marcus_, Jan 31 2023

%Y Cf. A140607, A039649, A140140, A138193, A138217, A138227, A138535, A138536, A138537, A138539, A140141, A000010, A000040, A140608, A138786.

%K nonn

%O 1,1

%A _Ray Chandler_, May 20 2008

%E More terms from _Michel Marcus_, Jan 31 2023