A047905 a(n+1) = a(n) + n (if n is even), a(n+1) = a(n) * n (if n is odd).

1, 1, 3, 9, 13, 65, 71, 497, 505, 4545, 4555, 50105, 50117, 651521, 651535, 9773025, 9773041, 166141697, 166141715, 3156692585, 3156692605, 66290544705, 66290544727, 1524682528721, 1524682528745, 38117063218625, 38117063218651

Offset: 1

Author

Miklos SZABO (mike(AT)ludens.elte.hu)

Keywords

• nonn
• easy
• nice

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A000124, A047904, A077138.

Programs

Haskell

a047905 n = a047905_list !! (n-1)
a047905_list = 1 : zipWith uncurry
                           (cycle [(*), (+)]) (zip a047905_list [1..])
-- Reinhard Zumkeller, Nov 13 2013, May 31 2011

Mathematica

a[0]=1;a[n_]:=a[n]=If[EvenQ[n],a[n-1]+n,a[n-1]n];Join[{1}, Array[a,40]] (* Harvey P. Dale, Apr 24 2011 *)
nxt[{n_,a_}]:={n+1,If[EvenQ[n],a+n,a*n]}; NestList[nxt,{1,1},30][[All,2]] (* Harvey P. Dale, Jul 27 2021 *)

Python

a=1
for n in range(1,33):
    print(a, end=", ")
    if n&1:
        a *= n
    else:
        a += n
# Alex Ratushnyak, Feb 24 2013