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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.
0
5, 31, 80, 121, 211, 341, 405, 496, 781, 1031, 1280, 1441, 1555, 1936, 2101, 2511, 2801, 3125, 3355, 3376, 4141, 4651, 4681, 5261, 5456, 6480, 6505, 6841, 7381, 7936, 8431, 9031, 9801, 9881, 11111, 11605, 12005, 12496, 13981, 14251, 15961, 16105, 16496, 17091, 17891
OFFSET
1,1
PROG
(Julia)
function isA299505(n)
n % 5 >= 2 && return false
n == 5 && return true
K = Int(floor(5.383*log(n)^1.161))
M = Int(floor(2*sqrt(n/3)))
for k in 3:K
for y in 2:M, x in 1:y
n == x^4+y*x^3+y^2*x^2+y^3*x+y^4 && return true
end end
return false
end
A299505list(upto) = [n for n in 1:upto if isA299505(n)]
println(A299505list(18000))
CROSSREFS
Cf. A024614, A002649 (subsequence of primes).
Sequence in context: A078686 A031908 A139862 * A102732 A213068 A138657
KEYWORD
nonn
AUTHOR
Peter Luschny, Mar 02 2018
STATUS
approved