[seqfan] A071974/A071975 rationals by prime factorization

[Kevin Ryde]

As a suggestion for A071974/A071975 rationals enumerated by prime
factors, a survey by David M. Bradley

    http://arxiv.org/abs/math/0509025

gives a couple of references which might precede Yoram Sagher's 1989
note referred to in A071974

    Kevin McCrimmon, Enumeration of the positive rationals, AMM Nov
    1960, p868, http://www.jstor.org/stable/2309448

    Gerald Freilich, A denumerability formula for the rationals, AMM Nov
    1965, p1013-1014, http://www.jstor.org/stable/2313350

Alas I don't have a library to read whether they're quite the same thing
as these seqs but perhaps someone else would be interested to take it
up.  David M. Bradley notes there's of course various choices for how
one might map positive integers <-> signed integers to encode the prime
powers.