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 A181836 #8 Jun 28 2013 05:07:15
%S A181836 1,1,1,1,1,3,1,5,15,35,7,21,35,385,165,143,1001,15015,5005,85085,
%T A181836 51051,46189,20995,440895,1616615,7436429,1716099,2860165,5311735,
%U A181836 15935205,7436429,215656441,3234846615
%N A181836 The product of primes <= n that are strongly prime to n.
%C A181836 k is strongly prime to n iff k is relatively prime to n and k does not divide n-1.
%H A181836 Peter Luschny, <a href="http://www.oeis.org/wiki/User:Peter_Luschny/StrongCoprimality">Strong coprimality</a>.
%e A181836 a(11) = 3 * 7 = 21.
%p A181836 with(numtheory):
%p A181836 Primes := n -> select(k->isprime(k),{$1..n}):
%p A181836 StrongCoprimes := n -> select(k->igcd(k,n)=1,{$1..n}) minus divisors(n-1):
%p A181836 StrongCoprimePrimes := n -> Primes(n) intersect StrongCoprimes(n):
%p A181836 A181836 := proc(n) local i; mul(i,i=StrongCoprimePrimes(n)) end:
%t A181836 a[n_] := Times @@ Select[Range[2, n], PrimeQ[#] && CoprimeQ[#, n] && !Divisible[n-1, #] &]; Table[a[n], {n, 0, 32}] (* _Jean-François Alcover_, Jun 28 2013 *)
%Y A181836 Cf. A181831, A181832, A181833, A181834, A181835, A001783.
%K A181836 nonn
%O A181836 0,6
%A A181836 _Peter Luschny_, Nov 17 2010