OFFSET
1,1
COMMENTS
All numbers in this sequence with three or more digits must have an odd number of digits. Any number with an even number of digits that follow this pattern is divisible by a number of the form 1010101...1010101 where the number of digits is one less than the number of digits in the original number.
Because A may equal B, 11 (and other prime repunits) are terms in this sequence (but not of A032758). - Harvey P. Dale, May 26 2015
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..135
EXAMPLE
121 = 11*11 is not prime and thus is not a term of this sequence.
MAPLE
select(isprime, [$0..99, seq(seq(seq(a*(10^(d+1)-10^(d+1 mod 2))/99 + b*(10^d - 10^(d mod 2))/99, b=0..9), a=1..9, 2), d=3..9, 2)]); # Robert Israel, Jul 08 2016
MATHEMATICA
Select[Union[Flatten[Table[FromDigits[PadRight[{}, n, #]], {n, 9}]&/@ Tuples[ Range[0, 9], 2]]], PrimeQ] (* Harvey P. Dale, May 26 2015 *)
PROG
(Python)
from itertools import count, islice
from sympy import isprime, primerange
def agen(): # generator of terms
yield from primerange(2, 100)
yield from (t for t in (int((A+B)*d2+A) for d2 in count(1) for A in "1379" for B in "0123456789") if isprime(t))
print(list(islice(agen(), 51))) # Michael S. Branicky, Jun 09 2022
CROSSREFS
KEYWORD
nonn,base
AUTHOR
J. Lowell, May 17 2014
STATUS
approved