OFFSET
1,1
EXAMPLE
If n=47 then 3547 is prime.
MAPLE
A055642 := proc(n) max(1, ilog10(n)+1) ; end: cat2 := proc(a, b) a*10^A055642(b)+b ; end: for n from 1 to 1000 do if isprime( cat2(35, n) ) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Jan 16 2009
MATHEMATICA
Select[Range[600], PrimeQ[FromDigits[Join[{3, 5}, IntegerDigits[#]]]]&] (* Harvey P. Dale, Jun 06 2015 *)
PROG
(Magma) [ n: n in [1..900] | IsPrime(Seqint(Intseq(n) cat [5, 3])) ]; // Vincenzo Librandi, Feb 03 2011
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Parthasarathy Nambi, Jun 07 2005
STATUS
approved