%I #7 Apr 14 2021 19:16:31
%S 3,4,4,444,827868,10387692,1885781034
%N a(n) is the smallest number m such that all n numbers m-1, m.m-1, ..., m.m. .. .m-1 are prime, where dot means concatenation.
%e All 4 numbers 444-1,444444-1,1+444444444-1,444444444444-1 are prime and 444
%e is the smallest such number so a(4)=444.
%p a:= proc(n) local m; for m do if andmap(isprime,
%p [seq(parse(cat(m$i))-1, i=1..n)]) then return m fi od
%p end:
%p seq(a(n), n=1..5); # _Alois P. Heinz_, Apr 14 2021
%o (Python)
%o from sympy import isprime
%o def A158962(n):
%o m = 1
%o while True:
%o for i in range(n):
%o if not isprime(int(str(m)*(i+1))-1):
%o break
%o else:
%o return m
%o m += 1 # _Chai Wah Wu_, Apr 14 2021
%Y Cf. A153434.
%K base,more,nonn
%O 1,1
%A _Farideh Firoozbakht_, Apr 02 2009