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 A105661 #11 Jul 05 2021 16:30:19
%S A105661 0,1,1,2,1,2,1,0,0,2,1,0,1,2,0,0,1,0,1,0,0,2,1,0,0,2,0,0,1,0,1,0,0,2,
%T A105661 0,0,1,2,0,0,1,0,1,0,0,2,1,0,0,0,0,0,1,0,0,0,0,2,1,0,1,2,0,0,0,0,1,0,
%U A105661 0,0,1,0,1,2,0,0,0,0,1,0,0,2,1,0,0,2,0,0,1,0,0,0,0,2,0,0,1,0,0,0,1,0,1,0,0
%N A105661 a(n)=1 if n is a prime, 2 if n is an even semiprime, otherwise 0.
%H A105661 Antti Karttunen, <a href="/A105661/b105661.txt">Table of n, a(n) for n = 1..10000</a>
%e A105661 a(3) = 1 because n = 3 is a prime;
%e A105661 a(4) = 2 because n = 4 = 2*2 is an even semiprime;
%e A105661 a(8) = 0 because n = 8 is neither prime nor an even semiprime.
%e A105661 a(15) = 0 because n = 15 = 3*5 is an odd semiprime.
%t A105661 Table[Which[PrimeQ[n],1,EvenQ[n]&&PrimeOmega[n]==2,2,True,0],{n,120}] (* _Harvey P. Dale_, Jul 05 2021 *)
%o A105661 (PARI) for(n=1,105,if((n%2==0)&&(bigomega(n)==2),r=2,r=isprime(n));print1(r,","))
%o A105661 (Scheme) (define (A105661 n) (cond ((= 1 (A001222 n)) 1) ((and (even? n) (= 2 (A001222 n))) 2) (else 0))) ;; _Antti Karttunen_, Jul 26 2017
%Y A105661 Cf. A001222, A001751, A105700.
%K A105661 easy,nonn
%O A105661 1,4
%A A105661 _Giovanni Teofilatto_, May 04 2005
%E A105661 Corrected and extended by _Rick L. Shepherd_, May 17 2005