OFFSET
1,2
LINKS
Michael S. Branicky, Table of n, a(n) for n = 1..10000
FORMULA
a(n) ~ n log n by the prime number theorem in arithmetic progressions. (These numbers are the primes mod 11, 33, 77, or 99 mod 100 with their last digit removed.) - Charles R Greathouse IV, Aug 27 2021
EXAMPLE
21 is a term because 211 is prime.
MATHEMATICA
upto=500; Select[Range[1, upto, 2], PrimeQ[FromDigits[Join[d=IntegerDigits[#], {Last[d]}]]]&]
PROG
(PARI) forprime(p=9, 1e4, if(p%100%11==0, print1(p\10", "))) \\ Charles R Greathouse IV, Aug 27 2021
(Python)
from sympy import isprime
def ok(n): return isprime(10*n + n%10)
print(list(filter(ok, range(388)))) # Michael S. Branicky, Aug 28 2021
CROSSREFS
KEYWORD
nonn,base,easy
AUTHOR
Paolo Xausa, Aug 27 2021
STATUS
approved