A181835 The sum of the primes <= n that are strongly prime to n.

0, 0, 0, 0, 0, 3, 0, 5, 8, 12, 7, 10, 12, 23, 19, 24, 31, 39, 36, 53, 51, 60, 54, 64, 72, 90, 80, 82, 88, 91, 90, 119, 127, 144, 127, 129, 143, 155, 139, 160, 174, 190, 185, 226, 225, 260, 248, 256

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 = 10.
		

Links

• Peter Luschny, Strong coprimality.

Crossrefs

Cf. A181830, A181831, A181832, A181834, A181836, A066911.

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):
A181835 := proc(n) local i; add(i,i=StrongCoprimePrimes(n)) end:

Mathematica

a[n_] := Select[Range[2, n], PrimeQ[#] && CoprimeQ[#, n] && !Divisible[n-1, #] &] // Total; Table[a[n], {n, 0, 47}] (* Jean-François Alcover, Jun 28 2013 *)