OFFSET
1,1
COMMENTS
Surprisingly there are only three(?) semiprimes sp, 10,14,15, such that sp minus its digits is semiprime.
EXAMPLE
15=3*5 and 15+1+5=21=3*7.
MATHEMATICA
Select[Range[500], Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[ #+Plus@@IntegerDigits[ # ]]==2&]
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Zak Seidov, Jun 14 2005
STATUS
approved