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Surprisingly there are only three(?) semiprimes sp, 10,14,15, such that sp minus its digits is semiprime.
Table of n, a(n) for n=1..54.
15=3*5 and 15+1+5=21=3*7.
Select[Range, Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[ #+Plus@@IntegerDigits[ # ]]==2&]
Sequence in context: A018888 A115174 A092783 * A076379 A227095 A038753
Adjacent sequences: A108635 A108636 A108637 * A108639 A108640 A108641
Zak Seidov, Jun 14 2005