# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a111928 Showing 1-1 of 1 %I A111928 #14 Jan 17 2016 12:47:42 %S A111928 1,3,2,7,21,42,48,18,26,234,2808,6552,7056,12096,96768,187488,3374784, %T A111928 7312032,29248128,307105344,467970048,8423460864,202163060736, %U A111928 101081530368,3133527441408,5061852020736,1499808006144,2999616012288,17997696073728,215972352884736 %N A111928 Numerator of f(n) := Product_{i=1..n} sigma(i)/i. %C A111928 _R. K. Guy_ observes (Nov 23 2005) that it appears that f(n) is an integer iff n = 1, 3, 8, 9, when f(n) = 1, 2, 18, 26 respectively. %H A111928 Harvey P. Dale, Table of n, a(n) for n = 1..808 %e A111928 1, 3/2, 2, 7/2, 21/5, 42/5, 48/5, 18, 26, 234/5, 2808/55, 6552/55, 7056/55, 12096/55, 96768/275, 187488/275, 3374784/4675, 7312032/4675, 29248128/17765, 307105344/88825, ... %p A111928 with(numtheory); f:=n->mul(sigma(i)/i,i=1..n); %t A111928 f[n_] := Numerator@ Product[ DivisorSigma[1, i]/i, {i, n}]; Array[f, 30] (* _Robert G. Wilson v_, May 01 2006 *) %t A111928 Numerator[FoldList[Times,Table[DivisorSigma[1,n]/n,{n,30}]]] (* _Harvey P. Dale_, Jan 17 2016 *) %Y A111928 Cf. A111934. %K A111928 nonn,frac %O A111928 1,2 %A A111928 _N. J. A. Sloane_, Nov 27 2005 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE