A155081 Primes p such that the largest digit of the concatenation of p and the p-th prime is a prime.

2, 3, 5, 7, 11, 31, 37, 47, 53, 67, 71, 73, 101, 113, 137, 173, 227, 233, 241, 257, 271, 307, 331, 347, 367, 521, 523, 557, 571, 577, 607, 613, 673, 727, 733, 743, 751, 1277, 1307, 1361, 1367, 1451, 1453, 1471, 1511, 1523, 1553, 1567, 1571, 1627, 1657, 1663

Offset

1,1

Links

Table of n, a(n) for n=1..52.

Example

2 is a term: 2 is prime, prime(2)=3, and the concatenation of 2 and 3 is 23, whose largest digit is 3 (a prime).
3 is a term: 3 is prime, prime(3)=5, and the concatenation of 3 and 5 is 35, whose largest digit is 5 (a prime).
7 is a term: 7 is prime, prime(7)=17, and their concatenation is 717, whose largest digit is 7 (a prime).

Maple

concat := proc (a, b) local bb: bb := nops(convert(b, base, 10)): 10^bb*a+b end proc: p := proc (n) local dig, ld: dig := convert(concat(n, ithprime(n)), base, 10): ld := max(seq(dig[j], j = 1 .. nops(dig))): if isprime(n) = true and isprime(ld) = true then n else end if end proc: seq(p(n), n = 1 .. 2000); # Emeric Deutsch, Jan 27 2009

Crossrefs

Cf. A000040, A006450.

Sequence in context: A028911 A028912 A075236 * A157158 A155833 A028867

Adjacent sequences: A155078 A155079 A155080 * A155082 A155083 A155084

Keyword

nonn,base

Author

Juri-Stepan Gerasimov, Jan 19 2009

Extensions

Corrected (added 5, removed 19, 59) and extended by Emeric Deutsch, Jan 27 2009

Example section edited by Jon E. Schoenfield, Jan 15 2019

Status

approved