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 A382073 #8 Mar 14 2025 20:23:29 %S A382073 4,22,121,202,301,1003,1111,2101,10003,10021,10102,10201,11002,11101, %T A382073 12001,30001,100021,100102,100201,101011,110002,110101,111001,200011, %U A382073 200101,1000021,1000111,1000201,1001002,1001101,1110001,2001001,3000001,10000003,10000021,10000201,10010002,10020001 %N A382073 Semiprimes with sum of digits 4. %H A382073 Robert Israel, <a href="/A382073/b382073.txt">Table of n, a(n) for n = 1..3655</a> %e A382073 a(3) = 121 is a term because 121 = 11^2 is a semiprime and its sum of digits is 1+2+1=4. %p A382073 qsemi:= proc(n) if numtheory:-bigomega(n) = 2 then n fi end proc: %p A382073 F:= proc(d) local i,j; %p A382073 seq(seq(qsemi(10^(d-1)+1 + 10^i + 10^j),i=0..j),j=0..d-1) %p A382073 end proc: %p A382073 map(F, [$1..10]); %t A382073 Select[Range[10^5],PrimeOmega[#]==2 && DigitSum[#]==4 &] (* _Stefano Spezia_, Mar 14 2025 *) %Y A382073 Intersection of A001358 and A052218. %Y A382073 Cf. A062339. %K A382073 nonn,base %O A382073 1,1 %A A382073 _Zak Seidov_ and _Robert Israel_, Mar 14 2025