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 A059826 a(n) = (n^2 - n + 1)*(n^2 + n + 1). 17
 1, 3, 21, 91, 273, 651, 1333, 2451, 4161, 6643, 10101, 14763, 20881, 28731, 38613, 50851, 65793, 83811, 105301, 130683, 160401, 194923, 234741, 280371, 332353, 391251, 457653, 532171, 615441, 708123, 810901, 924483, 1049601 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Main diagonal of A082039. - Paul Barry, Apr 02 2003 The base of the natural logarithms e = 2*Sum_{n>=0} 1/(a(n)*n!) and zeta(2) = Pi^2/6 = 1 + 2*Sum_{n>=1} (-1)^(n+1)/(a(n)*n^2). - Peter Bala, Jan 20 2008 LINKS Harry J. Smith, Table of n, a(n) for n = 0..1000 Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n) = n^4+n^2+1. - Paul Barry, Apr 02 2003 a(n) = (n^2-n+1) * (n^2+n+1) = A002061(n) * A002061(n+1), products of two consecutive central polygonal numbers. a(n) = (n^6-1)/(n^2-1), n>1. a(n) = (n^5-n^4+n^3-n^2+n-1)/(n-1) = A062159(n)/(n-1), n>1. - Alexander Adamchuk, Apr 12 2006 O.g.f.: (-1+2*x-16*x^2-6*x^3-3*x^4) / (x-1)^5. - R. J. Mathar, Feb 26 2008 a(n) = A219069(n,1), for n > 0. - Reinhard Zumkeller, Nov 11 2012 a(n+2) = (n^2+3n+3) * (n^2+5n+7) = (t(n)+t(n+2)) * (t(n+1)+t(n+3)), where t=A000217 are triangular numbers. For n>=1, a(n+2) = t(2*t(n+2)+t(n)) -t(t(n)-1). - J. M. Bergot, Nov 29 2012 4*a(n) = (n^2+n+1)^2+(n^2-n+1)^2+(n^2+n-1)^2+(n^2-n-1)^2. [Bruno Berselli, Jul 03 2014] a(n) = A002061(n^2). - Franklin T. Adams-Watters, Aug 01 2014 Sum_{n>=0} 1/a(n) = 1/2 + sqrt(3)*Pi*tanh(sqrt(3)*Pi/2)/6. - Amiram Eldar, Feb 14 2021 MAPLE with(combinat): seq(fibonacci(3, n)+n^4, n=0..40); # Zerinvary Lajos, May 25 2008 MATHEMATICA Table[n^4 + n^2 + 1, {n, 0, 50}] (* Wesley Ivan Hurt, Jun 09 2014 *) PROG (PARI) { for (n=0, 1000, f=n^2 + 1; write("b059826.txt", n, " ", (f - n)*(f + n)); ) } \\ Harry J. Smith, Jun 29 2009 (Magma) [n^4+n^2+1 : n in [0..50]]; // Wesley Ivan Hurt, Jun 09 2014 CROSSREFS Cf. A002061, A062159. Sequence in context: A071351 A083231 A129755 * A108970 A069017 A264246 Adjacent sequences: A059823 A059824 A059825 * A059827 A059828 A059829 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, Feb 24 2001 STATUS approved

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Last modified November 26 20:01 EST 2022. Contains 358362 sequences. (Running on oeis4.)