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A320603
a(0) = 1; if n is odd, a(n) = Product_{i=0..n-1} a(i); if n is even, a(n) = Sum_{i=0..n-1} a(i).
2
1, 1, 2, 2, 6, 24, 36, 20736, 20808, 8947059130368, 8947059171984, 716210897494804754044764041567551881216, 716210897494804754044764059461670225184
OFFSET
0,3
COMMENTS
Next term is too large to include.
Odd terms are the product of previous terms and even terms are the sum of previous terms.
FORMULA
a(n) = a(n-1) + 2*a(n-2), for even n > 2.
a(n) = a(n-1) * a(n-2)^2, for odd n > 1.
EXAMPLE
5 is odd, so a(5) = 1 * 1 * 2 * 2 * 6 = 24.
6 is even, so a(6) = 1 + 1 + 2 + 2 + 6 + 24 = 36.
MATHEMATICA
a[0]:= 1; a[n_]:= If[OddQ[n], Product[a[j], {j, 0, n-1}], Sum[a[j], {j, 0, n -1}]]; Table[a[n], {n, 0, 15}] (* G. C. Greubel, Oct 19 2018 *)
PROG
(PARI) first(n) = my(res = vector(n, i, 1)); for(x=3, n, res[x]=if(x%2, sum(i=1, x-1, res[i]), prod(i=1, x-1, res[i]))); res
(PARI) first(n) = my(res = vector(n, i, 1)); res[3]++; for(x=4, n, res[x]=if(x%2, res[x-1]+2*res[x-2], res[x-1]*res[x-2]^2)); res
CROSSREFS
Sum of previous terms: A011782.
Product of previous terms: A165420.
Sequence in context: A143084 A188962 A076741 * A276409 A093453 A301381
KEYWORD
nonn
AUTHOR
Iain Fox, Oct 17 2018
STATUS
approved