This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A108638 #11 Oct 02 2024 04:24:41 %S A108638 15,22,26,33,38,39,49,51,55,57,74,77,115,123,129,134,145,155,161,169, %T A108638 178,187,202,206,213,214,221,237,254,265,274,278,291,299,301,303,309, %U A108638 321,327,335,361,371,377,381,382,386,411,437,445,466,478,485,497,505 %N A108638 Semiprime plus its digits is semiprime. %C A108638 Members k of A001358 such that A062028(k) is in A001358. - _Robert Israel_, Oct 01 2024 %C A108638 Surprisingly there are only three(?) semiprimes sp, 10,14,15, such that sp minus its digits is semiprime. %C A108638 That is because n - (sum of its digits) = A066568(n) is divisible by 9. - _Robert Israel_, Oct 01 2024 %H A108638 Robert Israel, <a href="/A108638/b108638.txt">Table of n, a(n) for n = 1..10000</a> %e A108638 15=3*5 and 15+1+5=21=3*7. %p A108638 filter:= n -> numtheory:-bigomega(n) = 2 and numtheory:-bigomega(n+convert(convert(n,base,10),`+`))=2: %p A108638 select(filter, [$1..1000]); # _Robert Israel_, Oct 01 2024 %t A108638 Select[Range[500], Plus@@Last/@FactorInteger[ # ]==Plus@@Last/@FactorInteger[ #+Plus@@IntegerDigits[ # ]]==2&] %Y A108638 Cf. A001358, A062028, A066568. %K A108638 nonn,base %O A108638 1,1 %A A108638 _Zak Seidov_, Jun 14 2005