cp's OEIS Frontend

A255362 Numbers n such that neither n nor n+1 is representable as x*y+x+y, where x>=y>1.

%I A255362 #11 May 09 2021 11:18:08
%S A255362 0,1,2,3,4,5,6,9,12,21,36,45,57,60,72,81,105,156,165,177,192,225,261,
%T A255362 276,312,345,357,381,396,420,456,465,477,501,540,561,585,612,660,672,
%U A255362 717,732,756,837,861,876,885,981,996,1017,1092,1152,1185,1200,1212,1236,1281
%N A255362 Numbers n such that neither n nor n+1 is representable as x*y+x+y, where x>=y>1.
%C A255362 Indices of double zeros in A255361.
%o A255362 (Python)
%o A255362 TOP = 10000
%o A255362 a = [0]*TOP
%o A255362 for y in range(2, TOP//2):
%o A255362   for x in range(y, TOP//2):
%o A255362     k = x*y + x + y
%o A255362     if k>=TOP: break
%o A255362     a[k]+=1
%o A255362 print([n for n in range(TOP-1) if a[n]==0 and a[n+1]==0])
%o A255362 (PARI) iszero(n) = {for (y=2, n\2, for (x=y, n\2, if ((x*y+x+y) == n, return(0)););); return (1);}
%o A255362 isok(n) = iszero(n) && iszero(n+1); \\ _Michel Marcus_, Feb 22 2015
%Y A255362 Cf. A255361.
%K A255362 nonn
%O A255362 1,3
%A A255362 _Alex Ratushnyak_, Feb 21 2015