A306185 a(n) = (2n+1)!! + (2n)!! where k!! = A006882(k).

5, 23, 153, 1329, 14235, 181215, 2672145, 44781345, 840523635, 17465201775, 397983749625, 9867844134225, 264469801070475, 7618612476650175, 234748657653134625, 7703855828862818625, 268263758052098683875, 9879138385352252391375, 383608053176023482431625, 15664153113813817068080625

Offset: 1

Author

Alex Ratushnyak, Jan 27 2019

Keywords

• nonn

Examples

			a(3) = A006882(7) + A006882(6) = (7*5*3) + (6*4*2) = 105 + 48 = 153.
		

Crossrefs

Cf. A006882, A122649, A129890, A232617, A232618, A306184.

Programs

Python

o=e=1
for n in range(2, 99, 2):
  o*=n+1
  e*=n
  print(o+e, end=', ')

Formula

a(n) = A006882(2*n+1) + A006882(2*n).