A256230 Numbers n such that neither n nor 2*n is representable as x*y+x+y, where x>=y>1.

0, 1, 2, 3, 5, 6, 9, 18, 21, 30, 33, 36, 78, 81, 96, 105, 138, 141, 156, 165, 198, 210, 228, 261, 270, 273, 306, 330, 336, 345, 366, 378, 393, 438, 453, 498, 525, 546, 561, 576, 585, 600, 606, 618, 660, 690, 726, 765, 810, 828, 861, 876, 933, 936, 966, 996, 1005, 1008

Offset

1,3

Links

Table of n, a(n) for n=1..58.

Prog

(Python)
TOP = 2200
a = [0]*TOP
for y in range(2, TOP//2):
  for x in range(y, TOP//2):
    k = x*y + x + y
    if k>=TOP: break
    a[k]=1
print([n for n in range(TOP//2) if a[n]==0 and a[2*n]==0])

Crossrefs

Cf. A254636, A255362.

Cf. A064238 (also 3*n cannot be represented as x*y+x+y, x>=y>1).

Cf. A237189 (also 3*n and 4*n cannot be represented as x*y+x+y, x>=y>1).

Sequence in context: A240555 A102694 A124253 * A079371 A131761 A272776

Adjacent sequences: A256227 A256228 A256229 * A256231 A256232 A256233

Keyword

nonn

Author

Alex Ratushnyak, Mar 19 2015

Status

approved