OFFSET
0,3
COMMENTS
A coprime set of integers has (m,n)=1 for each pair of integers in the set.
REFERENCES
Alan Sutcliffe, Divisors and Common Factors in Sets of Integers, awaiting publication.
LINKS
Fausto A. C. Cariboni, Table of n, a(n) for n = 0..120
EXAMPLE
a(4)=20 since the 12 coprime subsets of (1,2,3,4) are ( ) (1) (2) (3) (4) (1,2) (1,3) (1,4) (2,3) (3,4) (1,2,3) (1,3 4) and these contain 20 elements.
PROG
(PARI) iscoprime(v) = {local(i); for (i=1, #v-1, for (j=i+1, #v, if (gcd(v[i], v[j]) != 1, return (0)); ); ); return (1); }
a(n) = {sn = vector(n, i, i); pset = vector(1<<#sn, i, vecextract(sn, i-1)); nb = 0; for (i=1, #pset, if (iscoprime(pset[i]), nb += #pset[i]); ); return (nb); } \\ Michel Marcus, Jul 12 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Alan Sutcliffe (alansut(AT)ntlworld.com), Aug 12 2003
EXTENSIONS
Terms a(38) and beyond from Fausto A. C. Cariboni, Oct 20 2020
STATUS
approved