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A227623 Numbers n such that phi(n) + pi(n) is prime. 1
2, 5, 6, 17, 18, 23, 24, 25, 31, 33, 36, 41, 47, 48, 51, 70, 75, 84, 87, 98, 106, 109, 111, 127, 130, 157, 160, 170, 180, 191, 192, 197, 211, 212, 217, 219, 220, 221, 233, 236, 241, 242, 244, 247, 248, 257, 258, 259, 260, 261, 278, 279, 286, 288, 290, 331, 333 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..1326

EXAMPLE

phi(786) + pi(786) = 260 + 137 = 397 which is prime, so 786 is in the sequence.

MAPLE

with(numtheory):K := proc(n) local a; a :=(phi(n)+ pi(n)); if  isprime(a)  then RETURN (n) fi: end: seq(K(n), n=1..1000); # K. D. Bajpai, Jul 18 2013

with(numtheory):K:=proc()local n, a, c;  c:=1; for n from 1 to 10000 do; a:=(phi(n)+ pi(n)); if  isprime(a)  then lprint(c, n); c:=c+1; fi; od; end: K(); # K. D. Bajpai, Jul 18 2013

MATHEMATICA

Select[Range[200], PrimeQ[EulerPhi[#] + PrimePi[#]] &] (* G. C. Greubel, Jul 04 2017 *)

CROSSREFS

Cf. A097646.

Sequence in context: A029939 A082198 A098871 * A146477 A166753 A319756

Adjacent sequences:  A227620 A227621 A227622 * A227624 A227625 A227626

KEYWORD

nonn,less

AUTHOR

K. D. Bajpai, Jul 18 2013

STATUS

approved

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Last modified September 23 16:36 EDT 2020. Contains 337314 sequences. (Running on oeis4.)