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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-Fran├žois 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

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