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 A272850 a(n) = (n^2 + (n+1)^2)*(n^2 + (n+1)^2 + 2*n*(n+1)). 1
 1, 45, 325, 1225, 3321, 7381, 14365, 25425, 41905, 65341, 97461, 140185, 195625, 266085, 354061, 462241, 593505, 750925, 937765, 1157481, 1413721, 1710325, 2051325, 2440945, 2883601, 3383901, 3946645, 4576825, 5279625 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Larger of pair of integers whose Pythagorean means are all integers. The smaller of the pairs are: (A001844). The arithmetic means are: (A007204) The geometric means are: (A005917) The harmonic means are: (A016754). Subtracting terms in A016754 from A007204 gives complementary harmonics (A060300). LINKS Seiichi Manyama, Table of n, a(n) for n = 0..10000 Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = (2*n^2 + 2*n + 1)*(4*n^2 + 4*n + 1). From Colin Barker, May 24 2016: (Start) a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) for n>4. G.f.: (1 + 40*x + 110*x^2 + 40*x^3 + x^4) / (1-x)^5. (End) PROG (PARI) a(n)=8*n^4 + 16*n^3 + 14*n^2 + 6*n + 1 \\ Charles R Greathouse IV, May 23 2016 (PARI) Vec((1+40*x+110*x^2+40*x^3+x^4)/(1-x)^5 + O(x^50)) \\ Colin Barker, May 24 2016 CROSSREFS Cf. A001844, A007204, A005917, A016754, A060300. Sequence in context: A093761 A324458 A073873 * A129153 A156719 A228059 Adjacent sequences: A272847 A272848 A272849 * A272851 A272852 A272853 KEYWORD nonn,easy AUTHOR Matthew Badley, May 07 2016 STATUS approved

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Last modified September 29 23:48 EDT 2023. Contains 365781 sequences. (Running on oeis4.)