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A320584
Numbers whose first digit is prime.
2
2, 3, 5, 7, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 217
OFFSET
1,1
MATHEMATICA
Select[Range@ 218, PrimeQ@ First@ IntegerDigits@ # &] (* Michael De Vlieger, Nov 05 2018 *)
PROG
(PARI) isok(n) = isprime(digits(n)[1]); \\ Michel Marcus, Oct 17 2018
(PARI) a(n) = n--; my (w=1); while (n >= 4*w, n -= 4*w; w*=10); w*prime(1+n\w) + (n%w) \\ Rémy Sigrist, Nov 16 2018
CROSSREFS
Supersequence of A320585 (primes whose first digit is prime).
Sequence in context: A048420 A048405 A110457 * A209191 A162948 A024768
KEYWORD
nonn,base
AUTHOR
Kritsada Moomuang, Oct 16 2018
STATUS
approved