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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
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS EXAMPLE 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). 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. 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

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Last modified April 14 22:47 EDT 2021. Contains 342971 sequences. (Running on oeis4.)