OFFSET
1,1
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..250
FORMULA
Conjectures from Colin Barker, Oct 24 2019: (Start)
G.f.: x*(4 + 2*x + 4*x^2 + 4*x^3 + 4*x^4 + 3*x^5 + 2*x^6 + x^7) / (1 - x)^2.
a(n) = 2*a(n-1) - a(n-2) for n>2.
a(n) = 24*(n-3) for n>6.
(End)
EXAMPLE
If you have 4 types of objects (coin denominations) you can have 35 different sets of 4. Out of these 35 only two have the same value: you can make 40 cents out of 4 dimes or out of a quarter and 3 nickels. Thus a(4) = 34.
PROG
(PARI) a(n) = {#select(k->k>0, Vec(polcoef(1/(1 - x*(y + y^5 + y^10 + y^25)) + O(x*x^n), n)))} \\ Andrew Howroyd, Oct 24 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Tanya Khovanova, Jul 28 2006
STATUS
approved