# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a120306 Showing 1-1 of 1 %I A120306 #4 Jan 29 2013 18:26:18 %S A120306 1,9,68,1364,12064,58303,4517375,1142991,4251679307,138473652271, %T A120306 240881487689,857560784067,49571162119157,12805922830496929, %U A120306 167798784068528807,365691567246838709,46160923354240494523 %N A120306 Numerator of the sum of all matrix elements of n X n matrix M[i,j]=CatalanNumber[i]/CatalanNumber[j], where CatalanNumber[k]=(2k)!/k!/(k+1)!=A000108[k]. %C A120306 p divides a(p-1) for primes p in A007645. %F A120306 a(n) = Numerator[Sum[Sum[(2i)!/(i!)^2/(i+1)/((2j)!/(j!)^2/(j+1)),{i,1,n}],{j,1,n}]]. %t A120306 Numerator[Table[Sum[Sum[(2i)!/(i!)^2/(i+1)/((2j)!/(j!)^2/(j+1)),{i,1,n}],{j,1,n}],{n,1,20}]] %Y A120306 Cf. A000108, A014138, A007645. %K A120306 frac,nonn %O A120306 1,2 %A A120306 _Alexander Adamchuk_, Jul 14 2006 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE