OFFSET
1,1
COMMENTS
The sequence is finite. Proof: Each 9-digit number has at least 15 nonprime substrings. Thus, each number with more than 9 digits has >= 15 nonprime substrings, too. Consequently, there is a boundary b<10^9, such that all numbers > b have more than 10 nonprime substrings.
LINKS
Hieronymus Fischer, Table of n, a(n) for n = 1..20230
EXAMPLE
a(1)=1000, since 1000 has 10 nonprime substrings (0, 0, 0, 1, 00, 00, 10, 000, 100, 1000).
a(20230)= 37337397, since there are 10 nonprime substrings (9, 33, 39, 7337, 7397, 73373, 373373, 733739, 7337397, 37337397).
CROSSREFS
KEYWORD
nonn,fini,base
AUTHOR
Hieronymus Fischer, Aug 26 2012
STATUS
approved