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 A109920 #10 Aug 08 2015 22:28:05
%S A109920 1,2,1,3,4,5,6,7,360,11,12,13,1680,17,18,19,4620,23,491400,29,30,31,
%T A109920 1884960,37,29640,41,42,43,45540,47,12994800,53,45821160,59,60,61,
%U A109920 89369280,67,164220,71,72,73,211110900,79,265680,83,195878760,89
%N A109920 a(1) = 1, then LCM of consecutive composite numbers sandwiched between primes.
%F A109920 a(2n) = prime(n) a(2n+1)= LCM of composite numbers between prime(n) and prime(n+1). a(1) = a(3) = 1 by choice.
%p A109920 A109920 := proc(n) local p; if n mod 2 = 0 then ithprime(n/2) ; elif n = 1 then 1 ; else p := ithprime((n-1)/2) ; lcm(seq(i,i=p+1..nextprime(p)-1)) ; fi ; end: for n from 1 to 80 do printf("%d, ",A109920(n)) ; od ; # _R. J. Mathar_, May 02 2007
%Y A109920 Cf. A109919.
%K A109920 easy,nonn
%O A109920 1,2
%A A109920 _Amarnath Murthy_, Jul 16 2005
%E A109920 More terms from _R. J. Mathar_, May 02 2007