A225156 Denominators of the sequence of fractions f(n) defined recursively by f(1) = 3/1; f(n+1) is chosen so that the sum and the product of the first n terms of the sequence are equal.
1, 2, 7, 67, 5623, 37772347, 1653794703916063, 3104205768420613437667191487267, 10767416908549848056705041797805600349527548164015760674541223
Offset: 1
Examples
f(n) = 3, 3/2, 9/7, 81/67, ... 3 + 3/2 = 3 * 3/2 = 9/2; 3 + 3/2 + 9/7 = 3 * 3/2 * 9/7 = 81/14; ...
Links
- Paul Yiu, Recreational Mathematics, Department of Mathematics, Florida Atlantic University, 2003, Chapter 5.4, p. 207 (Project).
Programs
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Maple
b:=n->3^(2^(n-2)); # n > 1 b(1):=3; p:=proc(n) option remember; p(n-1)*a(n-1); end; p(1):=1; a:=proc(n) option remember; b(n)-p(n); end; a(1):=1; seq(a(i),i=1..9);
Formula
a(n) = 3^(2^(n-2)) - product(a(i),i=1..n-1), n > 1 and a(1) = 1.
a(n) = 3^(2^(n-2)) - p(n) with a(1) = 1 and p(n) = p(n-1)*a(n-1) with p(1) = 1.
Comments