OFFSET
1,1
COMMENTS
Integers in this sequence can never be prime, as they are all multiples of 3. They can be semiprimes, as is the case for Prime(42) concatenated with Prime(50847544) = 1811000000181 = 3 x 603666666727.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
FORMULA
a(n) = Concatenate(P, P+1000000000) iff P prime and P+1000000000 prime.
EXAMPLE
181 is prime, 181+10^9 = 1000000181 is prime, so their concatenation is an element of this sequence: 1811000000181. Coincidentally, prime(181)+10^9 = 1000001087 is also prime.
MATHEMATICA
FromDigits[Join[IntegerDigits[#], IntegerDigits[#+10^9]]]&/@Select[Prime[ Range[ 200]], PrimeQ[ #+ 10^9]&] (* Harvey P. Dale, May 14 2022 *)
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Jonathan Vos Post, Mar 25 2005
STATUS
approved