OFFSET
1,1
EXAMPLE
Prime factors of 140 are 2, 5, and 7 and 257 is prime, so 140 is a term.
MATHEMATICA
Select[Range[220], Length[x=First/@FactorInteger[#]]>1&&PrimeQ[FromDigits[Flatten[IntegerDigits[x]]]]&]
PROG
(Python)
from sympy import isprime, primefactors
def ok(n):
pf = primefactors(n)
if len(pf) < 2: return False
return isprime(int("".join(str(p) for p in pf)))
print(list(filter(ok, range(2, 220)))) # Michael S. Branicky, Jun 12 2021
CROSSREFS
KEYWORD
nonn,base,less
AUTHOR
Jayanta Basu, Jun 04 2013
STATUS
approved