A320585 Primes whose first digit is prime.
2, 3, 5, 7, 23, 29, 31, 37, 53, 59, 71, 73, 79, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 503, 509, 521, 523, 541, 547, 557, 563, 569, 571
Offset: 1
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
2,3,5,7,seq(seq(op(select(isprime,[seq(i*10^(d-1)+j,j=1..10^(d-1)-1,2)])),i=[2,3,5,7]),d=1..4); # Robert Israel, Apr 02 2020
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Mathematica
Select[Range[575], PrimeQ[#] && PrimeQ[IntegerDigits[#][[1]]] &] (* Amiram Eldar, Nov 11 2018 *)
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PARI
isok(n) = isprime(n) && isprime(digits(n)[1]); \\ Michel Marcus, Oct 17 2018