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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 (list; graph; refs; listen; history; text; internal format)
 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. LINKS Iain Fox, Table of n, a(n) for n = 0..18 Iain Fox, Table of n, a(n) for n = 0..32 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:= 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++; 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 Cf. A039941, A077753, A122961. Sum of previous terms: A011782. Product of previous terms: A165420. Sequence in context: A143084 A188962 A076741 * A276409 A093453 A301381 Adjacent sequences:  A320600 A320601 A320602 * A320604 A320605 A320606 KEYWORD nonn AUTHOR Iain Fox, Oct 17 2018 STATUS approved

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Last modified June 18 18:52 EDT 2019. Contains 324215 sequences. (Running on oeis4.)