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 A087080 Number of elements in the coprime subsets of the integers 1 to n. 3
 0, 1, 4, 12, 20, 52, 60, 148, 196, 300, 332, 780, 828, 1904, 2080, 2348, 2812, 6352, 6608, 14736, 15632, 17456, 18640, 41152, 42432, 60912, 64800, 80928, 85408, 186304, 187584, 406400, 457344, 497472, 523456, 585280, 596288, 1284224 (list; graph; refs; listen; history; text; internal format)
 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 EXAMPLE a(4)=12 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 A087077 gives the number of elements in the primitive subsets. A084422 gives the number coprime subsets. A087081 gives the sum of the elements in coprime subsets. Sequence in context: A316299 A301231 A151914 * A134253 A115106 A270795 Adjacent sequences:  A087077 A087078 A087079 * A087081 A087082 A087083 KEYWORD nonn AUTHOR Alan Sutcliffe (alansut(AT)ntlworld.com), Aug 12 2003 STATUS approved

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Last modified February 17 11:57 EST 2019. Contains 320219 sequences. (Running on oeis4.)