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 A270433 #11 Mar 06 2025 08:17:42
%S A270433 0,0,0,0,0,1,2,2,2,2,3,3,3,4,5,5,5,6,7,7,8,9,10,11,11,11,11,12,12,12,
%T A270433 12,12,12,12,13,13,13,14,14,14,14,14,15,16,17,18,19,19,19,19,20,20,20,
%U A270433 21,22,23,24,24,25,26,27,27,28,28,28,29,30,30,30,31,32,33,34,34,34,35,35,36,37,37,37,37,38,39,39,40,41,42
%N A270433 a(n) = number of terms A270431 <= n; least monotonic left inverse of A270431.
%H A270433 Antti Karttunen, <a href="/A270433/b270433.txt">Table of n, a(n) for n = 1..35000</a>
%F A270433 a(1) = 0, for n > 1, a(n) = (A048673(n)-A064216(n) reduced modulo 2) + a(n-1).
%F A270433 Other identities. For all n >= 1:
%F A270433 a(n) = n - A270432(n).
%F A270433 a(A270431(n)) = n.
%t A270433 f[n_] := (Times @@ Power[If[# == 1, 1, NextPrime@ #] & /@ First@ #, Last@ #] + 1)/2 &@ Transpose@ FactorInteger@ n; g[n_] := Times @@ Power[If[# == 1, 1, NextPrime[#, -1]] & /@ First@ #, Last@ #] &@ Transpose@ FactorInteger[2 n - 1]; s = Select[Range@ 200, Xor[EvenQ@ f@ #, EvenQ@ g@ #] &] ; Table[Count[s, k_ /; k <= n], {n, 88}] (* _Michael De Vlieger_, Mar 17 2016 *)
%o A270433 (Scheme, with memoization-macro definec)
%o A270433 (definec (A270433 n) (if (<= n 1) 0 (+ (modulo (- (A048673 n) (A064216 n)) 2) (A270433 (- n 1)))))
%Y A270433 Cf. A048673, A064216, A270431, A270432, A270434.
%K A270433 nonn
%O A270433 1,7
%A A270433 _Antti Karttunen_, Mar 17 2016