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A166552 a(n) = 3*a(n-2) for n > 2; a(1) = 1; a(2) = 4. 3
1, 4, 3, 12, 9, 36, 27, 108, 81, 324, 243, 972, 729, 2916, 2187, 8748, 6561, 26244, 19683, 78732, 59049, 236196, 177147, 708588, 531441, 2125764, 1594323, 6377292, 4782969, 19131876, 14348907, 57395628, 43046721, 172186884, 129140163 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Interleaving of A000244 (powers of 3) and 4*A000244.

a(n) = A074324(n); A074324 has the additional term a(0)=1.

First differences are in A162852.

Second binomial transform is A054491. Fourth binomial transform is A153594.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..300

FORMULA

a(n) = (7+(-1)^n)*3^(1/4*(2*n-5+(-1)^n))/2.

G.f.: x*(1+4*x)/(1-3*x^2).

a(n+3) = a(n+2)*a(n+1)/a(n). - Reinhard Zumkeller, Mar 04 2011

a(n) = 3^floor((n-1)/2)*4^(1-n%2). - M. F. Hasler, Dec 03 2014

PROG

(MAGMA) [ n le 2 select 3*n-2 else 3*Self(n-2): n in [1..35] ];

(PARI) a(n)=3^(n\2)*(4/3)^!bittest(n, 0) \\ M. F. Hasler, Dec 03 2014

CROSSREFS

Equals A162766 preceded by 1.

Cf. A000244 (powers of 3), A074324, A162852, A054491, A153594.

Sequence in context: A168430 A074324 A162766 * A122804 A122544 A205371

Adjacent sequences:  A166549 A166550 A166551 * A166553 A166554 A166555

KEYWORD

nonn

AUTHOR

Klaus Brockhaus, Oct 16 2009

STATUS

approved

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Last modified December 19 04:51 EST 2014. Contains 252175 sequences.