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 A065101 a(0) = c, a(1) = p*c^3; a(n+2) = p*c^2*a(n+1) - a(n), for p = 3, c = 2. 1
 2, 24, 286, 3408, 40610, 483912, 5766334, 68712096, 818778818, 9756633720, 116260825822, 1385373276144, 16508218487906, 196713248578728, 2344050764456830, 27931895924903232, 332838700334381954 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS Harry J. Smith, Table of n, a(n) for n=0,...,100 Tanya Khovanova, Recursive Sequences J.-P. Ehrmann et al., Problem POLYA002, Integer pairs (x,y) for which (x^2+y^2)/(1+pxy) is an integer. Index entries for linear recurrences with constant coefficients, signature (12,-1). FORMULA G.f.: 2/(1-12*x+x^2). a(n) = 2*A004191(n). - R. J. Mathar, Sep 27 2014 MATHEMATICA a[0] = c; a[1] = p*c^3; a[n_] := a[n] = p*c^2*a[n - 1] - a[n - 2]; p = 3; c = 2; Table[ a[n], {n, 0, 20} ] PROG (PARI): polya002(3, 2, 18). For definition of function polya002 see A052530. (PARI) { p=3; c=2; k=p*c^2; for (n=0, 100, if (n>1, a=k*a1 - a2; a2=a1; a1=a, if (n, a=a1=k*c, a=a2=c)); write("b065101.txt", n, " ", a) ) } [From Harry J. Smith, Oct 07 2009] CROSSREFS Cf. A052530. Sequence in context: A221082 A002006 A230129 * A052739 A135389 A065513 Adjacent sequences:  A065098 A065099 A065100 * A065102 A065103 A065104 KEYWORD easy,nonn AUTHOR N. J. A. Sloane, Nov 12 2001 EXTENSIONS Gen. func. from Floor van Lamoen, Feb 07 2002 STATUS approved

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Last modified November 21 13:53 EST 2017. Contains 295001 sequences.