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 A378993 #32 Jan 11 2025 04:49:56 %S A378993 1,1,2,3,4,4,6,7,8,8,10,10,12,12,13,15,16,16,18,18,19,20,22,22,24,24, %T A378993 26,26,28,27,30,31,31,32,33,34,36,36,37,38,40,39,42,42,43,44,46,46,48, %U A378993 48,49,50,52,52,53,54,55,56,58,57,60,60,61,63,63,63,66,66 %N A378993 a(n) = n - omega(n), where omega = A001221. %F A378993 a(n) = n - A001221(n). %e A378993 a(40) = 38, since 40 has two distinct prime divisors (2 and 5), and so 40 - 2 = 38. %e A378993 a(41) = 40 also, since 41 is prime and therefore 41 - 1 = 40. %e A378993 a(42) = 39, since 42 has three distinct prime divisors (2, 3, 7), and so 42 - 3 = 39. %t A378993 a[n_]:=n-PrimeNu[n]; Array[a,68] (* _Stefano Spezia_, Dec 29 2024 *) %o A378993 (PARI) a(n) = n - omega(n); %Y A378993 Cf. A001221, A229109. %K A378993 nonn,easy %O A378993 1,3 %A A378993 _Torlach Rush_, Dec 17 2024