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A155081
Primes p such that the 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
OFFSET
1,1
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
Sequence in context: A028911 A028912 A075236 * A157158 A155833 A028867
KEYWORD
nonn,base
AUTHOR
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