A166481 a(n) = 3*a(n-2) for n > 2; a(1) = 1; a(2) = 7.

1, 7, 3, 21, 9, 63, 27, 189, 81, 567, 243, 1701, 729, 5103, 2187, 15309, 6561, 45927, 19683, 137781, 59049, 413343, 177147, 1240029, 531441, 3720087, 1594323, 11160261, 4782969, 33480783, 14348907, 100442349, 43046721, 301327047

Offset

1,2

Comments

Interleaving of A000244 and A005032.

Seventh binomial transform is A153598.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..200

Index entries for linear recurrences with constant coefficients, signature (0,3).

Formula

a(n) = (5+2*(-1)^n)*3^(1/4*(2*n-5+(-1)^n)).

G.f.: x*(1+7*x)/(1-3*x^2).

Mathematica

LinearRecurrence[{0, 3}, {1, 7}, 50] (* or *) Flatten[NestList[3#&, {1, 7}, 20]] (* Harvey P. Dale, Sep 24 2015 *)

Prog

(Magma) [ n le 2 select 6*n-5 else 3*Self(n-2): n in [1..34] ];

Crossrefs

Cf. A000244 (powers of 3), A005032 (7*3^n), A153598.

Sequence in context: A050013 A161417 A070409 * A050012 A271573 A098231

Adjacent sequences: A166478 A166479 A166480 * A166482 A166483 A166484

Keyword

nonn

Author

Klaus Brockhaus, Oct 14 2009

Status

approved