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 A109919 #13 Aug 08 2015 22:28:22
%S A109919 1,2,1,3,4,5,6,7,720,11,12,13,3360,17,18,19,9240,23,11793600,29,30,31,
%T A109919 45239040,37,59280,41,42,43,91080,47,311875200,53,549853920,59,60,61,
%U A109919 1072431360,67,328440,71,72,73,2533330800,79,531360,83,4701090240,89
%N A109919 a(1) = 1, then product of consecutive composite numbers sandwiched between primes.
%C A109919 a(1) = a(3) = 1 as empty product is defined to be 1.
%C A109919 The odd numbered terms are in A061214. - _T. D. Noe_, Oct 02 2012
%F A109919 a(2n) = prime(n) and a(2n+1)= product of composite numbers between prime(n) and prime(n+1).
%F A109919 a(2n) = A000040(n). a(2n+1) = A072472(n)/A000040(n+1). - _R. J. Mathar_, May 02 2007
%p A109919 A109919 := proc(n) local p; if n mod 2 = 0 then ithprime(n/2) ; elif n = 1 then 1 ; else p := ithprime((n-1)/2) ; mul(i,i=p+1..nextprime(p)-1) ; fi ; end: for n from 1 to 80 do printf("%d, ",A109919(n)) ; od ; # _R. J. Mathar_, May 02 2007
%Y A109919 Cf. A109920.
%Y A109919 Cf. A072472.
%Y A109919 Cf. A061214 (product of composite numbers between primes).
%K A109919 easy,nonn
%O A109919 1,2
%A A109919 _Amarnath Murthy_, Jul 16 2005
%E A109919 More terms from _R. J. Mathar_, May 02 2007