cp's OEIS Frontend

A264498 Numbers n that are the product of three distinct odd primes and x^2 + y^2 = n has integer solutions.

%I A264498 #11 Dec 09 2019 12:58:56
%S A264498 1105,1885,2405,2465,2665,3145,3445,3485,3965,4505,4745,5185,5365,
%T A264498 5785,5945,6205,6305,6409,6565,7085,7345,7565,7585,7685,8177,8245,
%U A264498 8585,8845,8905,9061,9265,9605,9685,9805,10205,10585,10865,11245,11285,11645,11713,11765
%N A264498 Numbers n that are the product of three distinct odd primes and x^2 + y^2 = n has integer solutions.
%C A264498 The three primes are of the form 4*k + 1.
%H A264498 Ray Chandler, <a href="/A264498/b264498.txt">Table of n, a(n) for n = 1..10000</a> (first 1000 terms from Colin Barker)
%e A264498 1105 is in the sequence because x^2 + y^2 = 1105 = 5*13*17 has solutions (x,y) = (4,33), (9,32), (12,31) and (23,24).
%o A264498 (PARI)
%o A264498 dop(d, nmax) = {
%o A264498   my(L=List(), v=vector(d,m,1)~, f);
%o A264498   for(n=1, nmax,
%o A264498     f=factorint(n);
%o A264498     if(#f~==d && f[1,1]>2 && f[,2]==v && f[,1]%4==v, listput(L, n))
%o A264498   );
%o A264498   Vec(L)
%o A264498 }
%o A264498 dop(3, 15000)
%Y A264498 Cf. A131574, A264499.
%K A264498 nonn
%O A264498 1,1
%A A264498 _Colin Barker_, Nov 15 2015