A026501 - OEIS

%I #21 Aug 11 2015 20:42:59

%S 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,

%T 48,57,58,60,70,72,78,85,88,93,100,102,105,112,120,130,133,145,148,

%U 165,168,177,190,210,217,221,232,240,253,254,262,263,267,273,277,280

%N 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.

%C Unlike A000926, this sequence is infinite. The first term not in A000926 is a(37) = 100. - _Ivan Neretin_, Jul 29 2015

%H Robert Israel, <a href="/A026501/b026501.txt">Table of n, a(n) for n = 1..4000</a>

%p N:= 1000: # to get all terms <= N

%p Allowed:= {$1..N}:

%p for count from 1 while Allowed <> {} do

%p   a:= min(Allowed);

%p   A[count]:= a;

%p   Allowed:= Allowed minus{a, seq(seq(A[i]*A[j]+(A[i]+A[j])*a,j=1..i-1),i=1..count-1)};

%p od:

%p seq(A[i],i=1..count-1); # _Robert Israel_, Aug 11 2015

%o (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);}

%o finda(va) = {na = vecmax(va) + 1; va = concat(va, na); while(! oka(va, #va), va[#va] = na++); na;}

%o 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

%Y Cf. A000926.

%K nonn

%O 1,2

%A _Clark Kimberling_

%E More terms from _Jud McCranie_