A211513 - OEIS

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A211513

Number of ordered triples (w,x,y) with all terms in {1,...,n} and 2*w^2=x*y.

0, 0, 2, 2, 4, 4, 6, 6, 10, 14, 16, 16, 18, 18, 20, 20, 24, 24, 32, 32, 34, 34, 36, 36, 40, 46, 48, 52, 54, 54, 56, 56, 66, 66, 68, 68, 76, 76, 78, 78, 82, 82, 84, 84, 86, 90, 92, 92, 96, 104, 118, 118, 120, 120, 128, 128, 132, 132, 134, 134, 136, 136, 138, 142

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

COMMENTS

For a guide to related sequences, see A211422.

LINKS

Table of n, a(n) for n=0..63.

MATHEMATICA

t[n_] := t[n] = Flatten[Table[2 w^2 - x*y, {w, 1, n}, {x, 1, n}, {y, 1, n}]]

c[n_] := Count[t[n], 0]

t = Table[c[n], {n, 0, 70}] (* A211513 *)

t/2 (* integers *)