A047904 a(n+1) = a(n) + n (if n is odd), a(n+1) = a(n) * n (if n is even).

1, 2, 4, 7, 28, 33, 198, 205, 1640, 1649, 16490, 16501, 198012, 198025, 2772350, 2772365, 44357840, 44357857, 798441426, 798441445, 15968828900, 15968828921, 351314236262, 351314236285, 8431541670840, 8431541670865, 219220083442490

Offset: 1

Author

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

Keywords

• nonn
• easy
• nice

Links

• T. D. Noe, Table of n, a(n) for n = 1..100

Crossrefs

Cf. A000124, A047905, A077138.

Programs

Haskell

a047904 n = a047904_list !! (n-1)
a047904_list = 1 : zipWith uncurry
                           (cycle [(+), (*)]) (zip a047904_list [1..])
-- Reinhard Zumkeller, Nov 13 2013, Mar 24 2013

Mathematica

Transpose[NestList[{#[[1]]+1,If[OddQ[#[[1]]],Total[#],Times@@#]}&,{1,1},30]][[2]] (* Harvey P. Dale, Sep 11 2012 *)

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