%I A002501 M5078 N2197
%S A002501 1,19,205,1795,14221,106819,778765,5581315,39606541,279447619,
%T A002501 1965098125,13792018435,96690872461,677427332419,4744368982285,
%U A002501 33220131761155,232579232659981,1628208214321219,11398072876175245
%N A002501 7^n-3*4^n+2*3^n.
%C A002501 Counts connected relations.
%D A002501 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%D A002501 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 
               (includes this sequence).
%D A002501 G. Kreweras, Inversion des polynomes de Bell bidimensionnels et application 
               au denombrement des relations binaires connexes. C. R. Acad. Sci. 
               Paris Ser. A-B 268 1969 A577-A579.
%Y A002501 Cf. A005333, A001047, A002502, A093732, A093733.
%Y A002501 Sequence in context: A113596 A155670 A085770 this_sequence A125407 A023017 
               A022647
%Y A002501 Adjacent sequences: A002498 A002499 A002500 this_sequence A002502 A002503 
               A002504
%K A002501 nonn,easy
%O A002501 1,2
%A A002501 N. J. A. Sloane (njas(AT)research.att.com).
%E A002501 Better definition and more terms from Goran Kilibarda, Vladeta Jovovic 
               (vladeta(AT)eunet.rs), Apr 14 2004