Search: id:A072948
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%I A072948
%S A072948 1,7,46,327,2350,17222,127508,952299
%N A072948 Number of permutations p of (1,2,3,...,2n) such that sum(k=1,2n,abs(k-p(k)))=2n.
%F A072948 This is impossible if the number of symbols is odd.
%o A072948 (PARI) a(n)=sum(k=1,n!,if(sum(i=1,n,abs(i-component(numtoperm(n,k),i)))-n,
               0,1))
%Y A072948 Cf. A072949.
%Y A072948 Sequence in context: A081894 A128597 A067318 this_sequence A000823 A036944 
               A068640
%Y A072948 Adjacent sequences: A072945 A072946 A072947 this_sequence A072949 A072950 
               A072951
%K A072948 more,nonn
%O A072948 1,2
%A A072948 Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 20 2002
%E A072948 One more term from Michel ten Voorde (seqfan(AT)tenvoorde.org) Jun 13 
               2003
%E A072948 17222 from Ryan Propper (rpropper(AT)stanford.edu), Mar 26 2007
%E A072948 2 more terms Sean A. Irvine (sairvin(AT)xtra.co.nz), Sep 22 2009

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