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 A213653 #30 Oct 27 2023 22:01:45
%S A213653 0,10,10001,21,4,14,6,25,26,9,46,38,39,49,77,69,169,278,0,289,299,489,
%T A213653 589,689,699,799,899,0,2899,3899,4989,5899,5999,6999,7999,9899,0,
%U A213653 19999,29999,48999,58999,68999,69999,88999,99899,0,299899,398999,589989
%N A213653 Least semiprime whose digital sum is n, or 0 if no such integer exists.
%C A213653 a(9k) = 0 for all k>1.
%C A213653 I conjecture that all terms > 278, except for 10001, end in the digit "9". What is the next term a(n) > 69 violating monotony, i.e., such that a(n) < a(n-1)? _M. F. Hasler_, Jun 17 2012
%C A213653 a(88) = 7999999999 < a(87) = 8899899999. - _Alois P. Heinz_, Jun 17 2012
%C A213653 a(76) = 499999999 < a(75) = 597999999. - _Donovan Johnson_, Jun 18 2012
%H A213653 Alois P. Heinz, <a href="/A213653/b213653.txt">Table of n, a(n) for n = 0..400</a> (first 101 terms from Donovan Johnson)
%t A213653 semiPrimeQ[n_] := PrimeOmega[n] == 2; t = Table[0, {100}]; k = 1; While[k < 10^7, If[ semiPrimeQ@ k, s = Plus @@ IntegerDigits@ k; If[s < 101 && t[[s]] == 0, t[[s]] = k; Print[{s, k}]]]; k++]
%o A213653 (PARI) A213653(n)={ n%9 || n==9 || return; forstep( a=A051885(n),9e9,9, bigomega(a)==2 || next; A007953(a)==n & return(a))} \\ - _M. F. Hasler_, Jun 17 2012
%K A213653 easy,base,nonn
%O A213653 0,2
%A A213653 _Robert G. Wilson v_, Jun 17 2012
%E A213653 a(0)-a(62) double-checked with given PARI code by _M. F. Hasler_, Jun 17 2012