A202237 - OEIS

%I #14 Aug 09 2015 01:07:10

%S 1,15,35,39,51,55,87,91,95,111,115,119,123,143,155,159,183,187,203,

%T 215,219,225,235,247,259,267,287,291,295,299,303,319,323,327,335,339,

%U 355,371,391,395,403,407,411,415,427,447,451,471,511,515,519,525,527,535,543,551

%N Odd numbers with the same number of prime factors of the form 4*k+1 and 4*k+3.

%C Primes are counted with multiplicity.

%C Closed under multiplication.

%p isA202237 := proc(n)

%p     if type(n,'odd') then

%p         A083025(n) = A065339(n) ;

%p     else

%p         false;

%p     end if;

%p end proc:

%p for n from 1 to 200 do

%p     if isA202237(n) then

%p         printf("%d,",n);

%p     end if;

%p end do: # _R. J. Mathar_, Dec 16 2011

%t fQ[n_]:=Plus@@((Mod[#[[1]],4]-2)*#[[2]]&/@If[==1,{},FactorInteger[n]]==0 && OddQ[n]; Select[Range[600],fQ] (* _Ray Chandler_, Dec 20 2011 *)

%o (PARI) netprime(n)=local(fm=factor(n));sum(k=1,matsize(fm)[1],if(fm[k,1]==2,0,if(fm[k,1]%4==1,fm[k,2],-fm[k,2])))

%o ap(n)=forstep(k=1,n,2,if(netprime(k)==0,print1(k", ")))

%Y A080774 (primitive elements), A072202 (even allowed).

%K nonn

%O 1,2

%A _Franklin T. Adams-Watters_, Dec 16 2011