OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Patrick De Geest, Home Primes
EXAMPLE
95 = 5*19 -> 519 = 3*173 -> 3173 = 19*167 -> 19167 = 3*6389 and 36389 is prime.
MAPLE
filter:= proc(n) local k, F, x, j;
x:= n;
for k from 1 to 4 do
if isprime(x) then return false fi;
F:= sort(ifactors(x)[2], (a, b) -> a[1]<b[1]);
F:= map(t -> t[1] $ t[2], F);
x:= F[1];
for j from 2 to nops(F) do
x:= x*10^(1+ilog10(F[j]))+F[j]
od;
od;
isprime(x)
end proc:
select(filter, [$2..1000]); # Robert Israel, Jun 25 2019
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Patrick De Geest, Jun 15 1998
EXTENSIONS
Edited by Charles R Greathouse IV, Apr 28 2010
STATUS
approved