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 A206011 #10 Nov 24 2022 16:39:40
%S A206011 0,0,0,9,9,9,18,18,18,18,27,27,27,27,27,36,36,45,45,45,45,54,54,54,63,
%T A206011 63,72,72,72,72,81,81,81,81,99,108,108,108,108,117,117,117,117,126,
%U A206011 126,135,135,135,135,135,144,144,144,153,153,153,162,162,171,171
%N A206011 The n-th semiprime minus its sum of digits.
%C A206011 This is to semiprimes A001358 as A068395 is to primes A000040. As with A068395, this is always a multiple of 9, hence cannot be prime. But, as happens first for a(4), a(n) can be semiprime.
%F A206011 a(n) = A001358(n) - A007953(A001358(n)).
%e A206011 a(4) = 10 - 1 = 9.
%e A206011 a(5) = 14 - 5 = 9.
%p A206011 read("transforms") :
%p A206011 A206011 := proc(n)
%p A206011 s := A001358(n) ;
%p A206011 s -digsum(s) ;
%p A206011 end proc: # _R. J. Mathar_, Sep 14 2012
%t A206011 #-Total[IntegerDigits[#]]&/@Select[Range[200],PrimeOmega[#]==2&] (* _Harvey P. Dale_, Nov 24 2022 *)
%Y A206011 Cf. A000040, A001358, A007953, A068395.
%K A206011 nonn,easy,base
%O A206011 1,4
%A A206011 _Jonathan Vos Post_, Feb 02 2012