cp's OEIS Frontend

A299505 Numbers of the form x^4 + y*x^3 + y^2*x^2 + y^3*x + y^4, where x and y are positive integers.

%I A299505 #5 Mar 02 2018 15:36:13
%S A299505 5,31,80,121,211,341,405,496,781,1031,1280,1441,1555,1936,2101,2511,
%T A299505 2801,3125,3355,3376,4141,4651,4681,5261,5456,6480,6505,6841,7381,
%U A299505 7936,8431,9031,9801,9881,11111,11605,12005,12496,13981,14251,15961,16105,16496,17091,17891
%N A299505 Numbers of the form x^4 + y*x^3 + y^2*x^2 + y^3*x + y^4, where x and y are positive integers.
%o A299505 (Julia)
%o A299505 function isA299505(n)
%o A299505     n % 5 >= 2 && return false
%o A299505     n == 5 && return true
%o A299505     K = Int(floor(5.383*log(n)^1.161))
%o A299505     M = Int(floor(2*sqrt(n/3)))
%o A299505     for k in 3:K
%o A299505         for y in 2:M, x in 1:y
%o A299505             n == x^4+y*x^3+y^2*x^2+y^3*x+y^4 && return true
%o A299505     end end
%o A299505     return false
%o A299505 end
%o A299505 A299505list(upto) = [n for n in 1:upto if isA299505(n)]
%o A299505 println(A299505list(18000))
%Y A299505 Cf. A024614, A002649 (subsequence of primes).
%K A299505 nonn
%O A299505 1,1
%A A299505 _Peter Luschny_, Mar 02 2018