A373978 - OEIS

%I #12 Jun 25 2024 13:12:43

%S 1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1,0,

%T 0,0,0,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,

%U 1,0,0,0,0,0,0,0,1,0,0,0,1,0,0,0,1,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,1,0,0,0,1

%N a(n) = 1 if n is a nonprime of the form 4*k + 1, otherwise 0.

%H Antti Karttunen, <a href="/A373978/b373978.txt">Table of n, a(n) for n = 1..100000</a>

%H <a href="/index/Ch#char_fns">Index entries for characteristic functions</a>

%t a[n_]:=Boole[!PrimeQ[n]&&Mod[n,4]==1]; Array[a,121](* _Stefano Spezia_, Jun 25 2024 *)

%o (PARI) A373978(n) = (!isprime(n) && 1==(n%4));

%Y Characteristic function of A091113.

%Y Cf. also A079260, A373977, A373979.

%K nonn

%O 1

%A _Antti Karttunen_, Jun 25 2024