%I M4494
%S 1,1,0,1,8,22,51,342,2609,16896,99114,876579,8551800,79595269,
%T 764804085,8905825760
%N Number of pairings {(b[1],c[1]),(b[2],c[2]),...,(b[n],c[n])} of the first 2n positive integers satisfying b[i] < c[i] and such that the 2n numbers c[i]+b[i] and c[i]b[i] are all distinct.
%C Huff paper has a typographical error, a(8)=2669.  _Sean A. Irvine_, Dec 14 2014
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%D R. Spira, Noncomplete residue systems, Problem 714, SIAM Rev., 14 (1972), 173ff.
%H R. K. Guy, <a href="/A002968/a002968_1.pdf">Letter to G. B. Huff & N. J. A. Sloane, Aug 1974</a>
%H G. B. Huff, <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa23/aa2322.pdf">On pairings of the first 2n natural numbers</a>, Acta Arithmetica, 23 (1973), 117126.
%H D. A. Klarner, <a href="/A002968/a002968.pdf">Letter to N. J. A. Sloane, Mar 1974</a>
%H R. Spira, <a href="/A002968/a002968_2.pdf">Noncomplete residue system Problem 714</a>, SIAM Rev., 14 (1972), 173174. (Annotated scanned copy)
%Y Cf. A007631.
%K nonn,more
%O 0,5
%A _N. J. A. Sloane_.
%E Better definition and values of a(11)a(15) from _Sean A. Irvine_, Dec 14 2014
%E a(0)=1 prepended by _Alois P. Heinz_, Oct 05 2018
