OFFSET
2,1
COMMENTS
There are d(n)*(d(n)-1)/2 sums of pairs of distinct positive divisors of n, where d(n) = number of positive divisors of n.
LINKS
Antti Karttunen, Table of n, a(n) for n = 2..65537
EXAMPLE
The positive divisors of 6 are 1,2,3,6. Letting d(m) = the number of positive divisors of m: d(1+2)=2; d(1+3)=3; d(1+6)=2; d(2+3)=2; d(2+6)=4; d(3+6)=3. The least of these values is 2, so a(6) = 2.
PROG
(PARI) { a(n) = d=divisors(n); m=numdiv(n+1); for(i=1, #d, for(j=i+1, #d, m=min(m, numdiv(d[i]+d[j])); )); m } \\ Max Alekseyev, Apr 27 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Jan 03 2008
EXTENSIONS
Extended by Max Alekseyev, Apr 27 2009
STATUS
approved