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

%I A256230 #10 May 10 2021 07:39:27
%S A256230 0,1,2,3,5,6,9,18,21,30,33,36,78,81,96,105,138,141,156,165,198,210,
%T A256230 228,261,270,273,306,330,336,345,366,378,393,438,453,498,525,546,561,
%U A256230 576,585,600,606,618,660,690,726,765,810,828,861,876,933,936,966,996,1005,1008
%N A256230 Numbers n such that neither n nor 2*n is representable as x*y+x+y, where x>=y>1.
%o A256230 (Python)
%o A256230 TOP = 2200
%o A256230 a = [0]*TOP
%o A256230 for y in range(2, TOP//2):
%o A256230   for x in range(y, TOP//2):
%o A256230     k = x*y + x + y
%o A256230     if k>=TOP: break
%o A256230     a[k]=1
%o A256230 print([n for n in range(TOP//2) if a[n]==0 and a[2*n]==0])
%Y A256230 Cf. A254636, A255362.
%Y A256230 Cf. A064238 (also 3*n cannot be represented as x*y+x+y, x>=y>1).
%Y A256230 Cf. A237189 (also 3*n and 4*n cannot be represented as x*y+x+y, x>=y>1).
%K A256230 nonn
%O A256230 1,3
%A A256230 _Alex Ratushnyak_, Mar 19 2015