A299505 - OEIS

%I #5 Mar 02 2018 15:36:13

%S 5,31,80,121,211,341,405,496,781,1031,1280,1441,1555,1936,2101,2511,

%T 2801,3125,3355,3376,4141,4651,4681,5261,5456,6480,6505,6841,7381,

%U 7936,8431,9031,9801,9881,11111,11605,12005,12496,13981,14251,15961,16105,16496,17091,17891

%N 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 (Julia)

%o function isA299505(n)

%o     n % 5 >= 2 && return false

%o     n == 5 && return true

%o     K = Int(floor(5.383*log(n)^1.161))

%o     M = Int(floor(2*sqrt(n/3)))

%o     for k in 3:K

%o         for y in 2:M, x in 1:y

%o             n == x^4+y*x^3+y^2*x^2+y^3*x+y^4 && return true

%o     end end

%o     return false

%o end

%o A299505list(upto) = [n for n in 1:upto if isA299505(n)]

%o println(A299505list(18000))

%Y Cf. A024614, A002649 (subsequence of primes).

%K nonn

%O 1,1

%A _Peter Luschny_, Mar 02 2018