OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1001
EXAMPLE
303 becomes 3(1)0(1)3 which is prime 31013.
MATHEMATICA
Select[Range[10, 500], PrimeQ[FromDigits[Riffle[IntegerDigits[#], 1]]]&] (* Harvey P. Dale, Apr 25 2019 *)
PROG
(PARI) is(n) = if(gcd(10, n%10) > 1 || n < 10, return(0)); my(d = digits(n), v = vector(2*#d - 1, i, if(i % 2 == 1, d[i>>1 + 1], 1))); isprime(fromdigits(v)) \\ David A. Corneth, Oct 15 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Aug 15 1999
EXTENSIONS
Offset set to 1 by Georg Fischer, Oct 15 2019
STATUS
approved