A364877 Numbers k such that 2*pi(k) + k is a prime number.

3, 5, 9, 17, 21, 23, 25, 31, 37, 41, 43, 45, 49, 57, 61, 65, 69, 85, 89, 91, 99, 103, 107, 109, 113, 119, 121, 129, 133, 135, 143, 151, 155, 159, 163, 165, 177, 185, 187, 191, 193, 195, 201, 213, 217, 219, 231, 235, 241, 243, 247, 251, 257, 267, 269, 273, 279

Offset

1,1

Comments

All terms of this sequence are odd.

A231232 lists the prime terms of this sequence.

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

k = 17 is a term: 2*pi(17) + 17 = 14 + 17 = 31, a prime number.

Maple

R:= NULL: count:= 0:
m:= 0:
for k from 1 while count < 100 do
  if isprime(k) then m:= m+1 fi;
  if isprime(2*m+k) then R:= R, k; count:= count+1 fi
od:
R; # Robert Israel, Oct 16 2023

Mathematica

Select[Range[280], PrimeQ[2*PrimePi[#] + #] &] (* Amiram Eldar, Aug 11 2023 *)

Prog

(PARI) isok(k) = isprime(2*primepi(k) + k); \\ Michel Marcus, Aug 12 2023

Crossrefs

Cf. A000720, A231232.

Sequence in context: A306973 A130114 A143106 * A217099 A276970 A294641

Adjacent sequences: A364874 A364875 A364876 * A364878 A364879 A364880

Keyword

nonn,easy

Author

Saish S. Kambali, Aug 11 2023

Extensions

More terms from Jon E. Schoenfield, Aug 11 2023

Status

approved