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 A025357 Numbers that are the sum of 4 nonzero squares in exactly 1 way. 13
 4, 7, 10, 12, 13, 15, 16, 18, 19, 20, 21, 22, 23, 25, 26, 27, 30, 33, 35, 38, 40, 44, 46, 48, 51, 53, 59, 62, 64, 65, 72, 80, 88, 89, 101, 104, 120, 152, 160, 176, 184, 192, 248, 256, 288, 320, 352, 416, 480, 608, 640, 704, 736, 768, 992, 1024, 1152, 1280, 1408, 1664 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Price, Table of n, a(n) for n = 1..95 Eric Weisstein's World of Mathematics, Square Number. FORMULA {n: A025428(n) = 1}. - R. J. Mathar, Jun 15 2018 A243148(a(n),4) = 1. - Alois P. Heinz, Feb 25 2019 MATHEMATICA selQ[n_] := Length[ Select[ PowersRepresentations[n, 4, 2], Times @@ # != 0 &]] == 1; Reap[Do[If[selQ[n], Print[n]; Sow[n]], {n, 1, 2000}]][[2, 1]] (* Jean-François Alcover, Oct 03 2013 *) 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, 4], {n, 0, 2000}], 1] - 1 // Flatten (* Jean-François Alcover, Nov 06 2020, after Alois P. Heinz in A243148 *) CROSSREFS Cf. A025428, A243148. Sequence in context: A211642 A127958 A000414 * A222949 A144020 A047845 Adjacent sequences:  A025354 A025355 A025356 * A025358 A025359 A025360 KEYWORD nonn AUTHOR STATUS approved

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Last modified January 26 03:55 EST 2021. Contains 340429 sequences. (Running on oeis4.)