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A074963 Max ( sigma(x*y) : 1<=x<=n, 1<=y<=n ).

%I A074963 #24 Feb 12 2018 10:24:55
%S A074963 1,7,13,31,42,91,96,127,195,234,234,403,403,480,576,744,744,847,847,
%T A074963 1170,1344,1344,1344,1651,1860,1860,1860,2240,2240,2880,2880,3048,
%U A074963 3048,3048,3048,4368,4368,4368,4368,5040,5040,5952,5952,5952,6552,6552,6552
%N A074963 Max ( sigma(x*y) : 1<=x<=n, 1<=y<=n ).
%C A074963 Does a(n)=sigma(n^2) for a finite number of values of n (1,2,3,4,6,8,12,18,24,60)? See A074964.
%H A074963 Reinhard Zumkeller, <a href="/A074963/b074963.txt">Table of n, a(n) for n = 1..750</a>
%p A074963 A074963 := proc(n)
%p A074963         a := 0 ;
%p A074963         for x from 1 to n do
%p A074963                 for y from 1 to x do
%p A074963                         a := max(a, numtheory[sigma](x*y)) ;
%p A074963                 end do:
%p A074963         end do;
%p A074963         a ;
%p A074963 end proc: # _R. J. Mathar_, Sep 27 2011
%t A074963 a[n_] := Module[{m = 0}, Do[m = Max[m, DivisorSigma[1, x*y]], {x, 1, n}, {y, 1, x}]; m]; Array[a, 50] (* _Jean-François Alcover_, Feb 12 2018 *)
%o A074963 (PARI) a(n)=vecmax(matrix(n,n,x,y, sigma(x*y)))
%o A074963 (Haskell)
%o A074963 a074963 n = maximum [a000203 (x*y) | x <- [1..n], y <- [x..n]]
%o A074963 -- _Reinhard Zumkeller_, Nov 14 2011
%Y A074963 Cf. A000203.
%K A074963 easy,nonn
%O A074963 1,2
%A A074963 _Benoit Cloitre_, Oct 05 2002