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 A025284 Numbers that are the sum of 2 nonzero squares in exactly 1 way. 17
 2, 5, 8, 10, 13, 17, 18, 20, 25, 26, 29, 32, 34, 37, 40, 41, 45, 52, 53, 58, 61, 68, 72, 73, 74, 80, 82, 89, 90, 97, 98, 100, 101, 104, 106, 109, 113, 116, 117, 122, 128, 136, 137, 146, 148, 149, 153, 157, 160, 162, 164, 169, 173, 178, 180, 181, 193, 194, 197, 202, 208, 212 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A025426(a(n)) = 1. - Reinhard Zumkeller, Aug 16 2011 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Square Number G. Xiao, Two squares FORMULA A243148(a(n),2) = 1. - Alois P. Heinz, Feb 25 2019 MATHEMATICA selQ[n_] := Length[ Select[ PowersRepresentations[n, 2, 2], Times @@ # != 0 &]] == 1; Select[Range[300], selQ] (* 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, 2], {n, 0, 300}], 1] - 1 // Flatten (* Jean-François Alcover, Nov 06 2020, after Alois P. Heinz in A243148 *) PROG (Haskell) import Data.List (elemIndices) a025284 n = a025284_list !! (n-1) a025284_list = elemIndices 1 a025426_list -- Reinhard Zumkeller, Aug 16 2011 CROSSREFS Cf. A000404, A025426, A081324, A125022, A018825, A001481, A007692, A243148. Sequence in context: A024509 A084889 A000404 * A140328 A000415 A172000 Adjacent sequences:  A025281 A025282 A025283 * A025285 A025286 A025287 KEYWORD nonn AUTHOR STATUS approved

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Last modified June 24 06:17 EDT 2021. Contains 345416 sequences. (Running on oeis4.)