OFFSET
1,1
COMMENTS
LINKS
Donovan Johnson, Table of n, a(n) for n = 1..605 (terms < 10^8; first 417 terms from T. D. Noe)
Eric Weisstein's World of Mathematics, Square Number.
FORMULA
A243148(a(n),3) = 1. - Alois P. Heinz, Feb 25 2019
MATHEMATICA
lim=20; nLst=Table[0, {lim^2}]; Do[n=a^2+b^2+c^2; If[n>0 && n<lim^2, nLst[[n]]++ ], {a, lim}, {b, a, Sqrt[lim^2-a^2]}, {c, b, Sqrt[lim^2-a^2-b^2]}]; Flatten[Position[nLst, 1]] (* T. D. Noe, Jun 06 2008 *)
b[n_, i_, k_, t_] := b[n, i, k, t] = If[n == 0, If[t == 0, 1, 0], If[i<1 || t<1, 0, b[n, i - 1, k, t] + If[i^2 > n, 0, b[n - i^2, i, k, t - 1]]]];
T[n_, k_] := b[n, Sqrt[n] // Floor, k, k];
Position[Table[T[n, 3], {n, 0, 200}], 1] - 1 // Flatten (* Jean-François Alcover, Nov 06 2020, after Alois P. Heinz in A243148 *)
PROG
(PARI) is(n)=if(n<11, return(n>0 && n%3==0)); if(n%4==0, return(is(n/4))); my(w); for(i=sqrtint((n-1)\3)+1, sqrtint(n-2), my(t=n-i^2); for(j=sqrtint((t-1)\2)+1, min(sqrtint(t-1), i), if(issquare(t-j^2), w++>1 && return(0)))); w \\ Charles R Greathouse IV, Aug 05 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved