OFFSET
1,3
REFERENCES
S. W. Golomb, personal communication, Svalbard, Norway, 7/97.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe).
EXAMPLE
{1}, {1/2}, {1/3,2/3}, {1/4,3/4}, {1/5,...,4/5}, {5/6}, ...
MATHEMATICA
a[1] = 1;
a[n_] := Sum[Boole[GCD[i, n] == 1 && Sum[t = i*n/d; Boole[GCD[t, d] == 1 && t < d < n], {d, Divisors[i*n]}] == 0], {i, 1, n - 1}];
Array[a, 100] (* Jean-François Alcover, Sep 05 2019, from PARI *)
PROG
(PARI) a(n)=if(n==1, 1, sum(i=1, n-1, gcd(i, n) == 1 && 0==sumdiv(i*n, d, my(t=i*n/d); gcd(t, d)==1 && d<n && t<d))) \\ Andrew Howroyd, Nov 16 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
Example corrected by and more terms from Olivier Gérard, February 1999
STATUS
approved