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 A270573 Let c be the n-th composite number. a(n) is the number of composites d < c such that c^(d-1) == 1 (mod d) and d^(c-1) == 1 (mod c). 3
 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 2, 0, 1, 0, 0, 0, 1, 0, 2, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 3, 0, 1, 0, 0, 6, 0, 1, 0, 1, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 1, 1, 0, 1, 0, 1, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,38 LINKS Felix Fröhlich, Table of n, a(n) for n = 1..10000 PROG (PARI) forcomposite(c=1, 100, my(i=0); forcomposite(d=1, c-1, if(Mod(c, d)^(d-1)==1 && Mod(d, c)^(c-1)==1, i++)); print1(i, ", ")) CROSSREFS Cf. A270574, A270575. Sequence in context: A070097 A202523 A215935 * A096271 A285640 A231189 Adjacent sequences:  A270570 A270571 A270572 * A270574 A270575 A270576 KEYWORD nonn AUTHOR Felix Fröhlich, Mar 19 2016 STATUS approved

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Last modified January 29 01:54 EST 2020. Contains 331328 sequences. (Running on oeis4.)