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A073457 Numbers n such that phi(n) = pi(n) + 2. 5
7, 9, 15, 16, 22, 54, 66, 120, 210 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A319877 A020939 A282758 * A067873 A217460 A347436
KEYWORD
fini,full,nonn
AUTHOR
Labos Elemer, Aug 02 2002
STATUS
approved

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Last modified March 19 07:40 EDT 2024. Contains 370958 sequences. (Running on oeis4.)