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 A329717 #8 Nov 24 2019 10:01:31 %S A329717 1,1,2,3,4,8,6,7,8,12,10,14,12,16,17,15,16,20,18,22,23,24,22,26,24,28, %T A329717 26,30,28,27,30,31,35,36,37,38,36,40,41,42,40,39,42,46,47,48,46,50,48, %U A329717 52,53,54,52,56,57,58,59,60,58,57,60,64,65,63,67,63,66 %N A329717 a(n) is n (plus or minus) the number of distinct primes dividing n according to parity (even or odd). %H A329717 Lars Blomberg, <a href="/A329717/b329717.txt">Table of n, a(n) for n = 1..10000</a> %F A329717 a(n) = n + A001221(n)*(-1)^A001221(n). %e A329717 A001221(3) = 1, so a(3) = 3-1 = 2. A001221(6) = 2, so a(6) = 6+2 = 8. %t A329717 Array[# + (om = PrimeNu[#]) * (-1)^om &, 67] (* _Amiram Eldar_, Nov 23 2019 *) %o A329717 (PARI) a(n) = my(om=omega(n)); n + (-1)^om*om; \\ _Michel Marcus_, Nov 20 2019 %Y A329717 Cf. A001221, A229109. %K A329717 nonn %O A329717 1,3 %A A329717 _Lars Blomberg_, Nov 20 2019