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 A076461 Sum of squares of numbers that can be written as t*n + u*(n+1) for nonnegative integers t,u in exactly two ways. 2
 13, 571, 5306, 26470, 93455, 264313, 640276, 1383276, 2736465, 5047735, 8796238, 14621906, 23357971, 36066485, 54076840, 79027288, 112909461, 158115891, 217490530, 294382270, 392701463, 516979441, 672431036, 865020100, 1101528025, 1389625263, 1737945846, 2156164906 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 REFERENCES Fred. Schuh, Vragen betreffende een onbepaalde vergelijking, Nieuw Tijdschrift voor Wiskunde, 52 (1964-1965) 193-198. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..1000 FORMULA a(n) = n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1)/6. G.f.: x*(13+480*x+1582*x^2+864*x^3+61*x^4)/(1-x)^7. MAPLE seq(1/6*n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1), n=1..30); MATHEMATICA CoefficientList[Series[(13 + 480 x + 1582 x^2 + 864 x^3 + 61 x^4)/(1 - x)^7, {x, 0, 50}], x] (* Vincenzo Librandi, Dec 30 2013 *) PROG (MAGMA) [n*(n+1)*(25*n^4+26*n^3-6*n^2-7*n+1)/6: n in [1..50]]; // Vincenzo Librandi, Dec 30 2013 CROSSREFS Cf. A076389, A076460-A076465. Sequence in context: A265503 A050286 A096761 * A168601 A142210 A109875 Adjacent sequences:  A076458 A076459 A076460 * A076462 A076463 A076464 KEYWORD easy,nonn AUTHOR Floor van Lamoen, Oct 13 2002 EXTENSIONS More terms from Vincenzo Librandi, Dec 30 2013 STATUS approved

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