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A181836 The product of primes <= n that are strongly prime to n. 10
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 (list; graph; refs; listen; history; text; internal format)
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

Table of n, a(n) for n=0..32.

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-Fran├žois Alcover, Jun 28 2013 *)

CROSSREFS

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

Sequence in context: A059616 A125053 A291665 * A124740 A347556 A338172

Adjacent sequences:  A181833 A181834 A181835 * A181837 A181838 A181839

KEYWORD

nonn

AUTHOR

Peter Luschny, Nov 17 2010

STATUS

approved

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Last modified May 18 10:09 EDT 2022. Contains 353807 sequences. (Running on oeis4.)