OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
EXAMPLE
a(2) = 4: the pairs (a,b) are (1,1), (1,2), (2,1), (2,2)
a(3) = 12: the pairs (a,b) are (1,3), (1,4), (1,6), (2,3), (2,4), (2,6), (3,1), (3,2), (4,1), (4,2), (6,1), (6,2)
PROG
(PARI) f(n, m=1) = { n==1 && return(1+(m<2)); my(p, q); sumdiv(n, d, if( d>=m && isprime(d+1), sum( i=0, valuation(q=n\d, p=d+1), f(q\p^i, p))))};
a(n) = sum(x=1, n-1, f(x)*f(n-x)); \\ Jinyuan Wang, May 03 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Jack Zhang, May 01 2019
EXTENSIONS
More terms from Jinyuan Wang, May 03 2019
STATUS
approved