A155548 Primes p such that p and the p-th prime have the same number of prime digits.

2, 3, 7, 17, 37, 47, 73, 83, 89, 97, 113, 163, 179, 193, 197, 251, 347, 359, 383, 397, 421, 431, 443, 487, 541, 547, 571, 593, 607, 617, 631, 653, 673, 677, 719, 727, 743, 751, 761, 787, 821, 829, 857, 877, 881, 883, 947, 971, 1009, 1013, 1019, 1021, 1051, 1087

Offset

1,1

Comments

Prime digit = 2, 3, 5 or 7.

Links

Table of n, a(n) for n=1..54.

Example

2 is a term because 2 is prime, prime(2)=3, and 2 and 3 each have 1 prime digit.
3 is a term because 3 is prime, prime(3)=5, and 3 and 5 each have 1 prime digit.
4 is not a term because 4 is not prime.
5 is prime, but prime(5)=11, and 5 has 1 prime digit while 11 has 0 prime digits, so 5 is not a term.

Maple

mm := proc (m) options operator, arrow: convert(m, base, 10) end proc: a := proc (n) local t, s, j: t := 0: s := 0: for j to nops(mm(n)) do if isprime(mm(n)[j]) = true then t := t+1 else end if end do: for j to nops(mm(ithprime(n))) do if isprime(mm(ithprime(n))[j]) = true then s := s+1 else end if end do: if isprime(n) = true and t = s then n else end if end proc: seq(a(n), n = 1 .. 1300); # Emeric Deutsch, Jan 28 2009

Crossrefs

Cf. A000040, A109066.

Sequence in context: A077007 A158498 A267601 * A191033 A105554 A145230

Adjacent sequences: A155545 A155546 A155547 * A155549 A155550 A155551

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 24 2009

Extensions

Corrected (added 761, 857; deleted 977) and extended by Emeric Deutsch, Jan 28 2009

Edited by Jon E. Schoenfield, Jan 20 2019

Status

approved