

A239060


Nonprime numbers whose divisors all appear as a substring in the number's decimal expansion.


3




OFFSET

1,2


COMMENTS

This is the subsequence of A239058 without the primes having a digit 1, A208270. It is thus a subsequence of A092911 (all divisors can be formed using the digits of the number) which is a subsequence of A011531 (numbers having the digit 1).
The term a(3)=17692313=A239058(870356), as well as the numbers 4482669527413081, 21465097175420089, and 567533481816008761 which are also members, were found by Charles R Greathouse IV, Mar 09 2014
The square of any term of A115738 is a member of this sequence. The above larger examples are of that form.


LINKS



EXAMPLE

The divisors of 17692313 are {1, 23, 769231, 17692313}; it can be seen that all of them occur as a substring in 17692313, therefore 17692313 is in this sequence.


PROG

(PARI) is(n)=!isprime(n)&&is_A239058(n)
(PARI) overlap(long, short)=my(D=10^#digits(short)); while(long>=short, if(long%D==short, return(1)); long\=10); 0
is(n)=my(d=divisors(n)); #d!=2 && !forstep(i=#d1, 1, 1, if(!overlap(n, d[i]), return(0))) \\ Charles R Greathouse IV, Mar 09 2014


CROSSREFS



KEYWORD

nonn,base,bref,more


AUTHOR



STATUS

approved



