A181835 - OEIS

%I #11 Jun 28 2013 05:07:23

%S 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,

%T 80,82,88,91,90,119,127,144,127,129,143,155,139,160,174,190,185,226,

%U 225,260,248,256

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

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

%H Peter Luschny, <a href="http://www.oeis.org/wiki/User:Peter_Luschny/StrongCoprimality">Strong coprimality</a>.

%e a(11) = 3 + 7 = 10.

%p with(numtheory):

%p Primes := n -> select(k->isprime(k),{$1..n}):

%p StrongCoprimes := n -> select(k->igcd(k,n)=1,{$1..n}) minus divisors(n-1):

%p StrongCoprimePrimes := n -> Primes(n) intersect StrongCoprimes(n):

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

%t 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 *)

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

%K nonn

%O 0,6

%A _Peter Luschny_, Nov 17 2010