[seqfan] Re: Reversing A281684.

[Hans Havermann]

MM (4 March 2021): "f(n) = least number k such that the concatenation of k composite numbers starting from the n-th composite is prime... Is it possible to find f(1), f(2), f(4), f(6) that are the first missing values for f() ?"

HH (5 March 2021): "f(6) = 14662"

I found no solutions in searches of f(1), f(2), and f(4) up to 62000. This gives any subsequent concatenation at least 300000 decimal digits.