OFFSET
3,1
LINKS
G. C. Greubel, Table of n, a(n) for n = 3..5000
Eric Weisstein's World of Mathematics, Graph Automorphism
Eric Weisstein's World of Mathematics, Prism Graph
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
a(4) = 48, otherwise a(n) = 4*n.
G.f.: 12*x^3 + 48*x^4 + 4*x^5*(5-4*x)/(1-x)^2. - R. J. Mathar, Jan 25 2016
E.g.f.: 4*x*(-3 - 3*x + x^3 + 3*exp(x))/3. - G. C. Greubel, May 31 2019
MATHEMATICA
LinearRecurrence[{2, -1}, {12, 48, 20, 24}, 60] (* Vincenzo Librandi, Jan 26 2016 *)
PROG
(PARI) Vec(12*x^3+48*x^4+4*x^5*(5-4*x)/(1-x)^2 + O(x^60)) \\ Altug Alkan, Jan 25 2016
(Magma) I:=[12, 48, 20, 24]; [n le 4 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..60]]; // Vincenzo Librandi, Jan 26 2016
(Sage) a=(12*x^3 + 48*x^4 + 4*x^5*(5-4*x)/(1-x)^2).series(x, 60).coefficients(x, sparse=False); a[3:] # G. C. Greubel, May 31 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Eric W. Weisstein, Oct 26 2006
STATUS
approved