OFFSET
1,17
REFERENCES
Keith F. Lynch, Posting to Math Fun Mailing List, Sep 19 2019.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..57
FORMULA
a(n) > 0 => n in { A140282 }. - Alois P. Heinz, Sep 29 2019
EXAMPLE
The unique smallest solution (for n = 13) is 1 + 9 + 25 + 36 + 81 + 121 = 16 + 49 + 64 + 144 = 4 + 100 + 169.
MAPLE
s:= proc(n) option remember; `if`(n<2, 0, n^2+s(n-1)) end:
b:= proc(n, x, y) option remember; `if`(n=1, 1, (p-> (l->
add(`if`(p>l[i], 0, b(n-1, sort(subsop(i=l[i]-p, l))
[1..2][])), i=1..3))([x, y, s(n)-x-y]))(n^2))
end:
a:= n-> `if`(irem(1+s(n), 3, 'q')=0, b(n, q-1, q)/2, 0):
seq(a(n), n=1..27); # Alois P. Heinz, Sep 29 2019
MATHEMATICA
s[n_] := s[n] = If[n < 2, 0, n^2 + s[n - 1]];
b[n_, x_, y_] := b[n, x, y] = Module[{p, l}, If[n == 1, 1, p = n^2; l = {x, y, s[n] - x - y}; Sum[If[p > l[[i]], 0, b[n - 1, Sequence @@ Sort[ ReplacePart[l, i -> l[[i]] - p]][[1 ;; 2]]]], {i, 1, 3}]]];
a[n_] := Module[{q, r}, {q, r} = QuotientRemainder[1 + s[n], 3]; If[r == 0, b[n, q - 1, q]/2, 0]];
Array[a, 30] (* Jean-François Alcover, Dec 04 2020, after Alois P. Heinz *)
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Sep 20 2019
EXTENSIONS
a(28)-a(45) from Alois P. Heinz, Sep 29 2019
a(46)-a(53) from Alois P. Heinz, Oct 05 2019
STATUS
approved