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 A109923 #12 Mar 07 2018 06:23:14 %S A109923 1,4,15,420,3960,80080,1225224,19399380,5354228880,145568097675, %T A109923 7600186994400,254425307479200,9957281351799600,392482839950100900, %U A109923 114779426083185063200,5474978624167927514640,312603618218620377448800 %N A109923 a(n) = lcm(1,2,3,...,prime(n))/(1 + 2 + ... + prime(n)). %F A109923 a(n) = A099795(n)/A006254(n-1). - _Andrey Zabolotskiy_, Mar 07 2018 %F A109923 a(n) = A056604(n)/A034953(n). - _Michel Marcus_, Mar 07 2018 %e A109923 a(4)=15 because the 4th prime is 7 and lcm(1,2,3,4,5,6,7)/(1+2+3+4+5+6+7) = 420/28 = 15. %p A109923 a:=n->lcm(seq(i,i=1..ithprime(n)))/sum(j,j=1..ithprime(n)): seq(a(n),n=2..20); # _Emeric Deutsch_, Jul 16 2005 %o A109923 (PARI) a(n) = lcm(vector(prime(n), k, k))/sum(k=1, prime(n), k); \\ _Michel Marcus_, Mar 07 2018 %Y A109923 Cf. A006254, A034953, A056604, A099795, A109922. %K A109923 easy,nonn %O A109923 2,2 %A A109923 _Amarnath Murthy_, Jul 16 2005 %E A109923 More terms from _Emeric Deutsch_, Jul 16 2005