login
A073457
Numbers n such that phi(n) = pi(n) + 2.
5
7, 9, 15, 16, 22, 54, 66, 120, 210
OFFSET
1,1
FORMULA
Solutions to A000010(x)=A000720(x)+k, where k=+2; finite for any fixed value of k.
EXAMPLE
8 primes below 22 = {2,3,5,7,11,13,17,19}; 10 terms in RRS[22]={1,3,5,7,9,13,15,17,19,21}, so 22 is here.
MAPLE
with(numtheory): A073457:=n->`if`(phi(n) = pi(n) + 2, n, NULL): seq(A073457(n), n=1..210); # Wesley Ivan Hurt, May 12 2015
MATHEMATICA
Do[s=EulerPhi[n]-PrimePi[n]; If[Equal[s, 2], Print[n]], {n, 10000}]
PROG
(Magma) [n: n in [2..1000] | EulerPhi(n) eq #PrimesUpTo(n)+2]; // Vincenzo Librandi, May 10 2015
CROSSREFS
KEYWORD
fini,full,nonn
AUTHOR
Labos Elemer, Aug 02 2002
STATUS
approved