A039941 Alternately add and multiply.
0, 1, 1, 1, 2, 2, 4, 8, 12, 96, 108, 10368, 10476, 108615168, 108625644, 11798392572168192, 11798392680793836, 139202068568601556987554268864512, 139202068568601568785946949658348, 19377215893777651167043206536157390321290709180447278572301746176
Offset: 0
Links
- Reinhard Zumkeller, Table of n, a(n) for n = 0..27
- A. V. Aho and N. J. A. Sloane, Some doubly exponential sequences, Fibonacci Quarterly, Vol. 11, No. 4 (1973), pp. 429-437.
- A. V. Aho and N. J. A. Sloane, Some doubly exponential sequences, Fibonacci Quarterly, Vol. 11, No. 4 (1973), pp. 429-437 (original plus references that F.Q. forgot to include - see last page!)
Programs
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Haskell
a039941 n = a039941_list !! (n-1) a039941_list = 0 : 1 : zipWith3 ($) (cycle [(+),(*)]) a039941_list (tail a039941_list) -- Reinhard Zumkeller, May 07 2012
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Mathematica
nxt[{n_,a_,b_}]:={n+1,b,If[EvenQ[n],a+b,a*b]}; Join[{0},Transpose[ NestList[ nxt,{0,0,1},20]][[3]]] (* Harvey P. Dale, Aug 23 2013 *) -
PARI
a(n)=if(n<2,n>0, if(n%2,a(n-1)*a(n-2),a(n-1)+a(n-2)))
Formula
a(2n) = a(2n-1) + a(2n-2); a(2n+1) = a(2n-1)*a(2n); a(0) = 0; a(1) = 1
a(n) = {a(n-1) + a(n-2), n even, a(n-1)*a(n-2), n odd}; a(0)=0; a(1)=1.
Extensions
Additional comments from Michael Somos, May 19 2000
One more term from Harvey P. Dale, Aug 23 2013