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 A163822 Number of divisors d of 2n such that gcd(d-1,2n/d-1) = 1. 2
 2, 1, 2, 2, 2, 4, 2, 2, 4, 4, 2, 6, 2, 2, 6, 4, 2, 6, 2, 4, 6, 4, 2, 8, 4, 2, 6, 6, 2, 10, 2, 2, 4, 4, 4, 10, 2, 2, 6, 8, 2, 10, 2, 4, 10, 4, 2, 8, 4, 4, 6, 6, 2, 10, 6, 4, 6, 4, 2, 12, 2, 2, 8, 6, 4, 10, 2, 4, 6, 10, 2, 12, 2, 2, 10, 6, 4, 8, 2, 6, 8, 4, 2, 14, 6, 2, 6, 4, 2, 16, 6, 4, 4, 4, 4, 12, 2, 2, 10 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The corresponding values for odd n are all zero, since then 2 is a common divisor of (d-1,n/d-1). LINKS Antti Karttunen, Table of n, a(n) for n = 1..10080 Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537 PROG (PARI) a(n)=local(d, r); r=0; d=divisors(2*n); for(k=1, #d, if(gcd(d[k]-1, 2*n\d[k]-1)==1, r++)); r CROSSREFS Cf. A000005, A163823. Sequence in context: A029170 A079526 A291708 * A029203 A159805 A208216 Adjacent sequences:  A163819 A163820 A163821 * A163823 A163824 A163825 KEYWORD nonn AUTHOR Franklin T. Adams-Watters, Aug 04 2009 STATUS approved

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Last modified May 18 19:58 EDT 2021. Contains 344002 sequences. (Running on oeis4.)