A073457 Numbers n such that phi(n) = pi(n) + 2.

7, 9, 15, 16, 22, 54, 66, 120, 210

Offset

1,1

Links

Table of n, a(n) for n=1..9.

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

Cf. A037228, A037171, A000010, A000720, A073455, A072456.

Sequence in context: A319877 A020939 A282758 * A067873 A217460 A347436

Adjacent sequences: A073454 A073455 A073456 * A073458 A073459 A073460

Keyword

fini,full,nonn

Author

Labos Elemer, Aug 02 2002

Status

approved