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%I #23 Feb 03 2022 09:32:26
%S 1,2,3,4,6,8,12,18,24,60
%N Numbers k such that Max ( sigma(x*y) : 1 <= x <= k, 1 <= y <= k ) = sigma(k^2).
%C Sequence is probably finite.
%C The next term in the sequence, if it exists, is larger than 40000. - _Stewart Gordon_, Sep 27 2011
%C Conjecture: subsequence of A066522, implying finiteness. - _Reinhard Zumkeller_, Nov 14 2011
%F A074963(a(n)) = A065764(a(n)). - _Reinhard Zumkeller_, Nov 14 2011
%p with(numtheory): s := proc(n) option remember: return sigma(n): end: a:= proc(n) option remember: if(n=0)then return 0: fi: return max(a(n-1),seq(s(x*n),x=1..n)): end: for n from 1 to 100 do if(a(n)=s(n^2))then printf("%d, ", n): end: od: # _Nathaniel Johnston_, Sep 26 2011
%o (Haskell)
%o a074964 n = a074964_list !! (n-1)
%o a074964_list = filter (\x -> a074963 x == a065764 x) [1..]
%o -- _Reinhard Zumkeller_, Nov 14 2011
%o (PARI) isok(k) = vecmax(setbinop((x,y)->sigma(x*y), [1..k])) == sigma(k^2); \\ _Michel Marcus_, Feb 03 2022
%Y Cf. A000203, A066522, A065764, A074963.
%K nonn,more
%O 1,2
%A _Benoit Cloitre_, Oct 05 2002
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