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 A088722 Number of divisors d>1 of n such that also d+1 divides n. 6
 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 2, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 4, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 3, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 2, 0, 0, 0, 1, 0, 1, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 COMMENTS a(A088723(n))>0, a(A088724(n))=1, a(A088725(n))=0; a(A088726(n))=n, a(k)<>n, for n < A088726(n). a(2n+1) = 0. - Ray Chandler, May 29 2008 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 EXAMPLE n=144: divisors(144) = {1,2,3,4,6,8,9,12,16,18,24,36,48,72,144}, there are a(144) = 3 divisors d>1 such that also d+1 divides 144: (2,3), (3,4) and (8,9). MATHEMATICA Table[DivisorSum[n, 1 &, And[# > 1, Divisible[n, # + 1]] &], {n, 105}] (* Michael De Vlieger, Jul 12 2017 *) PROG (PARI) A088722(n) = sumdiv(n, d, (d>1)&&!(n%(d+1))); \\ Antti Karttunen, Jul 12 2017 (PARI) first(n) = my(v = vector(n), k); for(i=2, sqrtint(n), k=i*(i+1); for(j=1, n\k, v[j*k]++); v \\ David A. Corneth, Jul 12 2017 CROSSREFS Cf. A088723, A088724, A088725, A088726, A129308. Sequence in context: A101638 A321379 A070141 * A122180 A033772 A086015 Adjacent sequences:  A088719 A088720 A088721 * A088723 A088724 A088725 KEYWORD nonn AUTHOR Reinhard Zumkeller, Oct 12 2003 EXTENSIONS Extended by Ray Chandler, May 29 2008 STATUS approved

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Last modified April 20 08:42 EDT 2019. Contains 322306 sequences. (Running on oeis4.)