Search: id:A145223
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%I A145223
%S A145223 0,0,6,0,90,420,3780,33264,333900,3670920,44054010,572697840,8017775766
%N A145223 a(n) is the number of odd permutations (of an n-set) with exactly 2 fixed 
               points.
%D A145223 Ali, Bashir and Umar, A., "Some combinatorial properties of the alternating 
               group". Southeast Asian Bulletin Math. 32 (2008), 823-830.
%F A145223 a(n)=(n(n-1)/2)*A145221(n-2), (n > 1)
%F A145223 Egf.: ((x^4)e^(-x))/4(1-x)
%e A145223 a(4) = 6 because there are exactly 6 odd permutations (of a 4-set) having 
               2 fixed points, namely: (12), (13), (14), (23), (24), (34).
%Y A145223 A145221
%Y A145223 Sequence in context: A051767 A156488 A057399 this_sequence A072129 A085511 
               A005212
%Y A145223 Adjacent sequences: A145220 A145221 A145222 this_sequence A145224 A145225 
               A145226
%K A145223 nonn
%O A145223 2,3
%A A145223 A. Umar (aumarh(AT)squ.edu.om), Oct 09 2008

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