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A213785 a(n) = Sum(P(i)*P(j), 1<=i<j<=n), where P(k) is the k-th Pell number A000129(k). 2
0, 0, 2, 17, 113, 693, 4123, 24234, 141738, 827298, 4824716, 28127435, 163955435, 955642695, 5569991317, 32464523892, 189217679988, 1102842830628, 6427842380918, 37464218883749, 218357488856453, 1272680757553593, 7417727160997231, 43233682460792670 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
Suggested by A190173.
LINKS
FORMULA
G.f.: x^2*(2-x)/((1-x)*(1-6*x+x^2)*(1-2*x-x^2)). [Bruno Berselli, Jun 20 2012]
a(n) = 9*a(n-1) -20*a(n-2) +8*a(n-3) +5*a(n-4) -a(n-5). - Vincenzo Librandi, Jun 20 2012
MATHEMATICA
LinearRecurrence[{9, -20, 8, 5, -1}, {0, 0, 2, 17, 113}, 30] (* Vincenzo Librandi, Jun 20 2012 *)
PROG
(Magma) I:=[0, 0, 2, 17, 113]; [n le 5 select I[n] else 9*Self(n-1)-20*Self(n-2)+8*Self(n-3)+5*Self(n-4)-Self(n-5): n in [1..30]]; // Vincenzo Librandi, Jun 20 2012
CROSSREFS
Sequence in context: A155845 A115354 A100274 * A198158 A203247 A294271
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jun 20 2012
STATUS
approved

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Last modified June 18 00:41 EDT 2024. Contains 373468 sequences. (Running on oeis4.)