A138524 a(n) = Sum_{k=1..n} (2*k)!.

2, 26, 746, 41066, 3669866, 482671466, 87660962666, 21010450850666, 6423384156578666, 2439325392333218666, 1126440053169940898666, 621574841786409380258666, 403913035968392044964258666, 305292257647682252546468258666

Offset: 1

Author

Leroy Quet, Mar 23 2008

Keywords

• easy
• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..224

Crossrefs

Cf. A007489, A007623, A138523, A138525, A163662.

Programs

Mathematica

Table[Sum[(2*i)!, {i,n}], {n,15}] (* Stefan Steinerberger, Mar 25 2008 *)
Accumulate[(2*Range[20])!] (* Harvey P. Dale, Nov 12 2016 *)

PARI

for(n=1,25, print1(sum(k=1,n, (2*k)!), ", ")) \\ G. C. Greubel, Sep 29 2017

Python

from math import factorial
def a(n): return sum(factorial(2*k) for k in range(1, n+1))
print([a(n) for n in range(1, 16)]) # Michael S. Branicky, Feb 26 2021

Formula

A007623(a(n)) = A163662(n). - Amiram Eldar, Apr 07 2022

Extensions

More terms from Stefan Steinerberger and Robert G. Wilson v, Mar 25 2008