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 A155081 Primes p such that largest digit of the concatenation of p and the p-th prime is a prime. 0

%I

%S 2,3,5,7,11,31,37,47,53,67,71,73,101,113,137,173,227,233,241,257,271,

%T 307,331,347,367,521,523,557,571,577,607,613,673,727,733,743,751,1277,

%U 1307,1361,1367,1451,1453,1471,1511,1523,1553,1567,1571,1627,1657,1663

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

%e 2 is a term: 2 is prime, prime(2)=3, and the concatenation of 2 and 3 is 23, whose largest digits is 3 (a prime).

%e 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).

%e 7 is a term: 7 is prime, prime(7)=17, and their concatenation is 717, whose largest digit is 7 (a prime).

%p 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

%Y Cf. A000040.

%K nonn,base

%O 1,1

%A _Juri-Stepan Gerasimov_, Jan 19 2009

%E Corrected (added 5, removed 19, 59) and extended by _Emeric Deutsch_, Jan 27 2009

%E Example section edited by _Jon E. Schoenfield_, Jan 15 2019

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Last modified May 11 19:29 EDT 2021. Contains 343808 sequences. (Running on oeis4.)