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 A171099 a(n) = number of solutions (x,y) (with 0<=x<=y) to x(x+1)/2 + y(y+1)/2 = n!. 1
 1, 1, 1, 2, 1, 2, 0, 1, 1, 1, 2, 0, 0, 1, 0, 2, 1, 2, 0, 0, 0, 2, 0, 0, 2, 0, 0, 8, 1, 2, 0, 0, 4, 4, 16, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 16, 0, 0, 0, 0, 1, 0, 0, 0, 0, 32, 0, 0, 0, 0, 0, 0, 2, 0, 16, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 16, 2, 4, 0, 0, 0, 2, 1, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS FORMULA a(n) = A000161(8*n!+2). - Max Alekseyev EXAMPLE Initial solutions are: (x,y,n) = (0,1,0), (0,1,1), (1,1,2), (0,3,3), (2,2,3), (2,6,4), (0,15,5), (5,14,5), (45,89,7), (89,269,8), (210,825,9), (760,2610,10), (1770,2030,10), none for n = 11 or 12, one for n = 13 (71504,85680,13) (found by Ed Pegg Jr), etc. CROSSREFS Cf. A000161, A152089 (n for which no solutions exist), A180590 (n for which solutions exist). Sequence in context: A120728 A092149 A303975 * A337253 A127173 A035160 Adjacent sequences:  A171096 A171097 A171098 * A171100 A171101 A171102 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 24 2010, based on a posting by R. K. Guy to the Sequence Fans Mailing List, Sep 10 2010 EXTENSIONS Corrected and extended (with data from G. Guninski, at the suggestion of N. J. A. Sloane) by D. S. McNeil, Sep 26 2010 STATUS approved

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Last modified May 13 04:09 EDT 2021. Contains 343836 sequences. (Running on oeis4.)