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URL: https://oeis.org/A073110

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A073110
Number of permutations p of (1,2,3,...,n) such that sigma(1+p(1))+sigma(2+p(2))+...+sigma(n+p(n))=2*n^2.
0
0, 1, 0, 2, 10, 37, 121, 725, 5160, 31794, 279136, 2137531, 21305316, 213311303, 2457648287, 30357607661, 387013387043, 5245097770693
OFFSET
1,4
COMMENTS
It seems that for any permutation p of (1,2,3,...,n) for n>3, the equation: sigma(1+p(1))+sigma(2+p(2))+...+sigma(n+p(n))=m*n^2 has solutions for m=2 only.
PROG
(PARI) a(n)=sum(k=1, n!, if(sum(i=1, n, sigma(i+component(numtoperm(n, k), i)))-2*n^2, 0, 1))
CROSSREFS
Sequence in context: A154323 A191349 A393238 * A034547 A246604 A124646
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Aug 19 2002
EXTENSIONS
2 more terms from Ryan Propper, Aug 27 2005
a(12)-a(18) from Robert Gerbicz, Nov 21 2010
STATUS
approved