Product-Over-Integers Expansion Of Real
Leroy Quet
qq-quet at mindspring.com
Thu Mar 18 21:55:43 CET 2004
Let A be a strictly increasing sequence of positive integers
where
sum{k=elements of A} 1/k
diverges.
For x = any real > 1,
we can find an infinite number of expansions (each a sub-sequence of A)
such that:
x = product{k=some elements of A} 1/(1-1/k)
But we can find the specific "greedy-algorithm" subsequence, where each
integer is chosen so that the partial-product remains <= x, and each new
term is the lowest unpicked element of A such that the partial product is
<= x.
(Such an expansion is, obviously, infinite if x is irrational.)
For example, either if A consists of all positive integers >= 2 or
consists of just the primes, then, for x = pi, we have the expansion's
terms
2, 3, 23,...
(pi = 1/(1-1/2) *1/(1-1/3) *1/(1-1/23) *...,
if I calculated right.)
I guess we can also ask about the subsequences of A such that
x = product{k=some elements of A} (1 + 1/k).
I bet this idea is not new. Are any such expansions already in the
Encyclopedia of Integer Sequences?
Is there anything else known about such expansions?
thanks,
Leroy Quet
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