[seqfan] Reversing A281684.

[michel.marcus at free.fr]

Dear Seqfans 


A281684 is defined as: Least composite k such that the concatenation of n consecutive composites, starting from k, is a prime. 
It has a few small values: A281684(2)= 8; A281684(6)= 14; A281684(14)= 15; A281684(24)= 18; A281684(302)= 16. 


So is it possible to reverse it ? 
f(n) = least number k such that the concatenation of k composite numbers starting from the n-th composite is prime 


f(3) = 2 2nd composite : 8 ; 89 is prime 
f(5) = 646 
f(7) = 6 7th composite : 14 ; 141516182021 is prime 
f(8) = 14 
f(9) = 302 
f(10) = 24 


Is it possible to find f(1), f(2), f(4), f(6) that are the first missing values for f() ? 


Best 
MM