A155501 Numbers n such that n^2 is of form x^2+40y^2 with positive x,y.

7, 11, 13, 14, 19, 21, 22, 23, 26, 28, 33, 35, 37, 38, 39, 41, 42, 44, 46, 47, 49, 52, 53, 55, 56, 57, 59, 63, 65, 66, 69, 70, 74, 76, 77, 78, 82, 84, 88, 89, 91, 92, 94, 95, 98, 99, 103, 104, 105, 106, 110, 111, 112, 114, 115, 117, 118, 119, 121, 123, 126, 127, 130, 131

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Maple

N:= 1000: # to get all terms <= N
g:= proc(t) local r; if t^2 > 40*y^2 then return NULL fi;
r:= t/2 + 20*y^2/t; if r::integer and r <= N then r fi; end proc:
R:= {}:
for y from 1 to floor(N/sqrt(40)) do
  R:= R union map(g, numtheory:-divisors(40*y^2))
od:
sort(convert(R, list)); # Robert Israel, Jul 16 2018

Crossrefs

Cf. A155500 (numbers of form x^2+40y^2 with positive x, y).

Sequence in context: A187040 A028784 A119393 * A271500 A271499 A235336

Adjacent sequences: A155498 A155499 A155500 * A155502 A155503 A155504

Keyword

nonn

Author

Zak Seidov, Jan 23 2009

Status

approved