A127847 a(n)=4^C(n,2)*(4^n-1)/3.

0, 1, 20, 1344, 348160, 357564416, 1465657589760, 24017731997138944, 1574098141758535761920, 412645105639632468417970176, 432690992231222540584116394393600, 1814838857553600260569028862094736359424, 30447948962887853884238295543591323273401466880

Offset: 0

Author

Paul Barry, Feb 02 2007

Keywords

• easy
• nonn

Comments

-a(n) is the Hankel transform of A127846, the series reversion of x/(1+5x+4x^2). Note that (4^n-1)/3 has g.f. x/(1-5x+4x^2).

Programs

Mathematica

Table[4^Binomial[n,2] (4^n-1)/3,{n,0,20}] (* Harvey P. Dale, Aug 29 2015 *)

Extensions

More terms from Harvey P. Dale, Aug 29 2015