A181836 The product of primes <= n that are strongly prime to n.

1, 1, 1, 1, 1, 3, 1, 5, 15, 35, 7, 21, 35, 385, 165, 143, 1001, 15015, 5005, 85085, 51051, 46189, 20995, 440895, 1616615, 7436429, 1716099, 2860165, 5311735, 15935205, 7436429, 215656441, 3234846615

Offset: 0

Author

Peter Luschny, Nov 17 2010

Keywords

• nonn

Comments

k is strongly prime to n iff k is relatively prime to n and k does not divide n-1.

Examples

			a(11) = 3 * 7 = 21.
		

Links

• Peter Luschny, Strong coprimality.

Crossrefs

Cf. A181831, A181832, A181833, A181834, A181835, A001783.

Programs

Maple

with(numtheory):
Primes := n -> select(k->isprime(k),{$1..n}):
StrongCoprimes := n -> select(k->igcd(k,n)=1,{$1..n}) minus divisors(n-1):
StrongCoprimePrimes := n -> Primes(n) intersect StrongCoprimes(n):
A181836 := proc(n) local i; mul(i,i=StrongCoprimePrimes(n)) end:

Mathematica

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 *)