The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A215935 Ordered pairs of primes (p, q) dividing n for which p^e = 1 mod q, where e is the exponent of p in n. 2
 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2, 0, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 0, 0, 1, 0, 2, 0, 1, 1, 1, 0, 3, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 1, 2, 1, 1, 0, 3, 0, 1, 1, 0, 0, 2, 0, 1, 0, 2, 0, 1, 0, 1, 1, 1, 0, 3, 0, 2, 0, 1, 0, 4, 0, 1, 0, 1, 0, 2, 0, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 COMMENTS If n in A056867 then a(n) = 0. LINKS Alois P. Heinz, Table of n, a(n) for n = 1..10000 EXAMPLE 12 is divisible by two primes, 2 and 3. The exponent of 2 is 2 and the exponent of 3 is 1. 2^2 = 1 mod 3 and 3^1 = 1 mod 2, so a(12) = 2. MAPLE a:= proc(n) local l; l:= ifactors(n)[2];        add(add(`if`(irem(i[1]^i[2], j[1])=1, 1, 0), i=l), j=l)     end: seq (a(n), n=1..100);  # Alois P. Heinz, Aug 28 2012 MATHEMATICA a[n_] := With[{f = FactorInteger[n]}, Sum[ Boole[ Mod[p[[1]]^p[[2]], q[[1]]] == 1], {p, f}, {q, f}]]; Table[a[n], {n, 1, 93}] (* Jean-François Alcover, Sep 03 2012 *) PROG (PARI) a(n)=my(f=factor(n), k=#f[, 1]); sum(i=1, k, sum(j=1, k, i!=j&&f[i, 1]^f[i, 2]%f[j, 1]==1)) CROSSREFS Cf. A054395, A056867. Sequence in context: A161520 A070097 A202523 * A270573 A096271 A285640 Adjacent sequences:  A215932 A215933 A215934 * A215936 A215937 A215938 KEYWORD nonn AUTHOR Charles R Greathouse IV, Aug 27 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 17 14:57 EST 2020. Contains 330958 sequences. (Running on oeis4.)