A025939 Expansion of 1/((1-2*x)*(1-3*x)*(1-6*x)*(1-9*x)).

1, 20, 265, 2960, 30301, 295340, 2795905, 25996520, 238988101, 2181067460, 19810829545, 179385327680, 1620996705901, 14628147660380, 131888407103185, 1188406175868440, 10704118783463701, 96387848642218100, 867795316487968825, 7811985924125490800, 70318841781990301501, 632935386858454884620

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..900

Index entries for linear recurrences with constant coefficients, signature (20,-135,360,-324).

Formula

a(n) = -6^(n+1)-2^(n+1)/7+3^(n+1)/2+9^(n+2)/14. - R. J. Mathar, Jun 04 2013

a(n) = 3^(n+1)-2^(n+1)+15*a(n-1)-54*a(n-2). - Vincenzo Librandi, Apr 30 2026

Mathematica

a[0]=1; a[1]=20; a[n_]:=a[n]=3^(n+1)-2^(n+1)+15*a[n-1]-54*a[n-2]; Table[a[n], {n, 0, 21}] (* Vincenzo Librandi, Apr 30 2026 *)

Prog

(Magma) I:=[1, 20]; [n le 2 select I[n] else 3^n-2^n+15*Self(n-1)-54*Self(n-2): n in [1..22]]; // Vincenzo Librandi, Apr 30 2026

Crossrefs

Sequence in context: A278408 A229562 A021854 * A278773 A021824 A125455

Adjacent sequences: A025936 A025937 A025938 * A025940 A025941 A025942

Keyword

nonn,easy

Author

N. J. A. Sloane

Extensions

More terms from Vincenzo Librandi, Apr 30 2026

Status

approved