A077138 a(0) = 0. If n is odd, a(n) = a(n-1) + n, otherwise a(n) = a(n-1) * n.

0, 1, 2, 5, 20, 25, 150, 157, 1256, 1265, 12650, 12661, 151932, 151945, 2127230, 2127245, 34035920, 34035937, 612646866, 612646885, 12252937700, 12252937721, 269564629862, 269564629885, 6469551117240, 6469551117265, 168208329048890

Offset: 0

Author

Amarnath Murthy, Oct 30 2002

Keywords

• nonn
• easy

Links

• William Boyles, Table of n, a(n) for n = 0..1000 [Terms 0 through 26 were computed by Amarnath Murthy; terms 27 through 1000 were computed by William Boyles, Nov 27 2016]

Crossrefs

Cf. A047904, A047905, A222559.

Programs

Mathematica

a = 0; Table[If[OddQ[n], a = n + a, a = n*a], {n, 0, 30}] (* T. D. Noe, Feb 26 2013 *)
nxt[{n_,a_}]:={n+1,If[EvenQ[n],a+n+1,a(n+1)]}; NestList[nxt,{0,0},30][[All,2]] (* Harvey P. Dale, Feb 13 2022 *)

PARI

a(n)=if(n<0,0,if(n%2,n+a(n-1),n*a(n-1)))

Python

a=0
for n in range(1, 33):
    print(a, end=', ')
    if n&1:
        a += n
    else:
        a *= n

Formula

a(0) = 0, a(2n) = 2n*a(2n-1) and a(2n+1) = a(2n) +(2n +1).

Extensions

Name improved by T. D. Noe, Feb 26 2013