A026501 a(n) = least positive integer > a(n-1) and not a(j)*a(k) + a(k)*a(i) + a(i)*a(j) for 1<=i<j<k<n.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 15, 16, 18, 21, 22, 24, 25, 28, 30, 33, 37, 40, 42, 45, 48, 57, 58, 60, 70, 72, 78, 85, 88, 93, 100, 102, 105, 112, 120, 130, 133, 145, 148, 165, 168, 177, 190, 210, 217, 221, 232, 240, 253, 254, 262, 263, 267, 273, 277, 280

Offset

1,2

Comments

Unlike A000926, this sequence is infinite. The first term not in A000926 is a(37) = 100. - Ivan Neretin, Jul 29 2015

Links

Robert Israel, Table of n, a(n) for n = 1..4000

Maple

N:= 1000: # to get all terms <= N
Allowed:= {$1..N}:
for count from 1 while Allowed <> {} do
  a:= min(Allowed);
  A[count]:= a;
  Allowed:= Allowed minus{a, seq(seq(A[i]*A[j]+(A[i]+A[j])*a, j=1..i-1), i=1..count-1)};
od:
seq(A[i], i=1..count-1); # Robert Israel, Aug 11 2015

Prog

(PARI) oka(va, nv) = {for (i=1, nv, for (j=i+1, nv, for (k=j+1, nv, if (va[nv] == va[j]*va[k] + va[k]*va[i] + va[i]*va[j], return (0)); ); ); ); return (1); }
finda(va) = {na = vecmax(va) + 1; va = concat(va, na); while(! oka(va, #va), va[#va] = na++); na; }
lista(nn) = {va = [1]; print1(1, ", "); for (n=1, nn, na = finda(va); print1(na, ", "); va = concat(va, na); ); va; } \\ Michel Marcus, Aug 10 2015

Crossrefs

Cf. A000926.

Sequence in context: A033110 A049812 A093668 * A000926 A011875 A249575

Adjacent sequences: A026498 A026499 A026500 * A026502 A026503 A026504

Keyword

nonn

Author

Clark Kimberling

Extensions

More terms from Jud McCranie

Status

approved