OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
The prime, 3 has an index of 2, i.e.; pi(3) = 2 and the concatenation, 23 is a prime.
MATHEMATICA
Select[ Prime@ Range@ 273, PrimeQ@ FromDigits@ Join[ IntegerDigits@ PrimePi@#, IntegerDigits@# ] &]
Select[Table[{n, Prime[n]}, {n, 300}], PrimeQ[#[[1]]*10^IntegerLength[ #[[2]]]+ #[[2]]]&][[All, 2]] (* Harvey P. Dale, Jun 01 2017 *)
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Robert G. Wilson v, Oct 10 2009
STATUS
approved