OFFSET
1,2
COMMENTS
The difference between this problem and A005840 and A051045 is the word "at most". In this problem, at most n different resistors are used to generate all possible resistances using in series and in parallel wirings, also including resistances where some of the resistors from the collection 1,2,...,n, are not used.
FORMULA
a(n) = 2 * A005840(n) + n - 2, n > 1.
E.g.f.: exp(x)*(-2*exp(x) + exp(x)*x + 2)/(-2 + exp(x)).
MAPLE
a:= n-> n!* coeff(series(exp(x)*(-2*exp(x) +
exp(x)*x + 2)/(-2 + exp(x)), x, n+1), x, n):
seq(a(n), n=1..25);
CROSSREFS
KEYWORD
nonn,uned
AUTHOR
I. N. Galidakis (jgal(AT)ath.forthnet.gr), Nov 28 2006
STATUS
approved