OFFSET
1,2
COMMENTS
There are roughly 5/(18m log 10) * 10^m terms of this sequence up to 10^m: all primes between 10^k and 2*10^k, half the primes between 3*10^k and 4*10^k, 3/5 of the primes between 7*10^k and 8*10^k, and 1/4 of the primes between 9*10^k and 10*10^k for all 1 < k < m, using the prime number theorem in arithmetic progressions. Thus the "probability" that a random number up to 10^m is in this sequence is 0.12/m.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
20 is a term because prime(20)=71, prime(21)=73, and 17 is a prime.
MATHEMATICA
cldfdQ[{a_, b_}]:=PrimeQ[FromDigits[Join[{Mod[a, 10]}, {First[IntegerDigits[b]]}]]]; Position[ If[cldfdQ[#], 1, 0]&/@Partition[Prime[Range[200]], 2, 1], 1]//Flatten (* Harvey P. Dale, Apr 26 2022 *)
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Zak Seidov, Jul 09 2003
EXTENSIONS
Comment from Charles R Greathouse IV, Apr 27 2010
STATUS
approved