This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A073087 #15 Feb 28 2019 11:35:36 %S A073087 1,6,30,210,30030,223092870,13082761331670030, %T A073087 3217644767340672907899084554130, %U A073087 1492182350939279320058875736615841068547583863326864530410 %N A073087 Least k such that sigma(k^k)>=n*k^k. %C A073087 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 A073087 Note that sigma(k^k) = prod (p^(k r + 1) - 1)/(p - 1). - _Mitch Harris_, Sep 14 2005 %C A073087 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 A073087 David W. Wilson, <a href="/A073087/a073087.txt">Comments on this sequence</a> %F A073087 a(n) = A091440(n)# = A002110(A112873(n)) for n >= 4. %o A073087 (PARI) a(n)=if(n<0,0,s=1; while(sigma(s^s)<n*s^s,s++); s) %Y A073087 Cf. A023199. %K A073087 nonn %O A073087 1,2 %A A073087 _Benoit Cloitre_, Aug 18 2002 %E A073087 More terms from _David W. Wilson_, Sep 15 2005