A047681 - OEIS

%I #20 Sep 08 2022 08:44:57

%S 6,-54,2106,-179334,26414586,-5957217414,1906398972666,

%T -821369346492294,458382160232420346,-321645776191296739974,

%U 277173760840187306341626,-287758284647458145849816454,354245505704926834826124160506,-510230879113388713374134585497734

%N a(n) = 3^(2*n)*(3^(2*n)-1)*Bernoulli(2*n)/(2*n).

%D J. W. Milnor and J. D. Stasheff, Characteristic Classes, Princeton, 1974, p. 283.

%H <a href="/index/Be#Bernoulli">Index entries for sequences related to Bernoulli numbers.</a>

%t Table[3^(2 n) (3^(2 n) - 1) BernoulliB[2 n] / (2 n), {n, 25}] (* _Vincenzo Librandi_, Apr 08 2020 *)

%o (PARI) a(n) = 3^(2*n)*(3^(2*n)-1)*bernfrac(2*n)/(2*n); \\ _Michel Marcus_, Mar 07 2020

%o (Magma) [3^(2*n)*(3^(2*n) - 1)*Bernoulli(2*n) / (2*n):n in [1..30]]; // _Vincenzo Librandi_, Apr 08 2020

%K sign

%O 1,1

%A _N. J. A. Sloane_