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%I #15 Feb 28 2019 11:35:36
%S 1,6,30,210,30030,223092870,13082761331670030,
%T 3217644767340672907899084554130,
%U 1492182350939279320058875736615841068547583863326864530410
%N Least k such that sigma(k^k)>=n*k^k.
%C Does a(n) = the product of primes less than or equal to prime(n+1) = A002110(n+1)? Answer from Lambert Klasen (Lambert.Klasen(AT)gmx.net), Sep 14 2005: No, this is not true.
%C Note that sigma(k^k) = prod (p^(k r + 1) - 1)/(p - 1). - _Mitch Harris_, Sep 14 2005
%C I have proved to my own satisfaction that for n >= 4, A073087(n) = p#, where p is the smallest prime satisfying p#/phi(p#) >= n. See link. - _David W. Wilson_, Sep 14 2005
%H David W. Wilson, <a href="/A073087/a073087.txt">Comments on this sequence</a>
%F a(n) = A091440(n)# = A002110(A112873(n)) for n >= 4.
%o (PARI) a(n)=if(n<0,0,s=1; while(sigma(s^s)<n*s^s,s++); s)
%Y Cf. A023199.
%K nonn
%O 1,2
%A _Benoit Cloitre_, Aug 18 2002
%E More terms from _David W. Wilson_, Sep 15 2005