OFFSET
1,8
FORMULA
a(n) = Sum_{p=1..floor(n/8)} Sum_{o=p..floor((n-p)/7)} Sum_{m=o..floor((n-o-p)/6)} Sum_{l=m..floor((n-m-o-p)/5)} Sum_{k=l..floor((n-l-m-o-p)/4)} Sum_{j=k..floor((n-k-l-m-o-p)/3)} Sum_{i=j..floor((n-j-k-l-m-o-p)/2)} (c(i) + c(j) + c(k) + c(l) + c(m) + c(o) + c(p) + c(n-i-j-k-l-m-o-p)), where c(x) = [gcd(n,x) = 1] and [ ] is the Iverson bracket.
EXAMPLE
The partitions of 11 into 8 parts are: 1+1+1+1+1+1+1+4, 1+1+1+1+1+1+2+3, and 1+1+1+1+1+2+2+2. 11 is coprime to parts 1, 2, 3 and 4. Since there are 24 total parts in these partitions that are coprime to 11, a(11) = 24.
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, May 27 2023
STATUS
approved