OFFSET
0,6
COMMENTS
k is strongly prime to n iff k is relatively prime to n and k does not divide n-1.
LINKS
Peter Luschny, Strong coprimality.
EXAMPLE
a(11) = 3 * 7 = 21.
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 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Peter Luschny, Nov 17 2010
STATUS
approved