cp's OEIS Frontend

A232749 Inverse function to Hofstadter's A030124.

%I A232749 #12 Dec 09 2021 11:54:53
%S A232749 0,1,0,2,3,4,0,5,6,7,8,0,9,10,11,12,13,0,14,15,16,17,18,19,20,0,21,22,
%T A232749 23,24,25,26,27,28,0,29,30,31,32,33,34,35,36,37,0,38,39,40,41,42,43,
%U A232749 44,45,46,47,0,48,49,50,51,52,53,54,55,56,57,58,59,0,60
%N A232749 Inverse function to Hofstadter's A030124.
%C A232749 This is an inverse function for Hofstadter's A030124 in the sense that for all n, n = a(A030124(n)). a(n) = 0 when n is not in A030124, but instead in its complement A005228.
%C A232749 Note that A232747(n)*a(n) = 0 for all n.
%C A232749 Used to compute the permutation A232751.
%H A232749 <a href="/index/Ho#Hofstadter">Index entries for Hofstadter-type sequences</a>
%t A232749 nmax = 100; A5228 = {1};
%t A232749 Module[{d = 2, k = 1}, Do[While[MemberQ[A5228, d], d++];
%t A232749      k += d; d++; AppendTo[A5228, k], {n, 1, nmax}]];
%t A232749 a46[n_] := For[k = 1, True, k++, If[A5228[[k]] > n, Return[k - 1]]];
%t A232749 a48[n_] := a48[n] = If[n == 1, 0, a48[n-1] + (1 - (a46[n] - a46[n - 1]))];
%t A232749 a[n_] := If[n == 1, 0, a48[n] (a48[n] - a48[n - 1])];
%t A232749 Array[a, nmax] (* _Jean-François Alcover_, Dec 09 2021 *)
%o A232749 (Scheme, with memoization macro definec from Antti Karttunen's IntSeq-library)
%o A232749 (definec (A232749 n) (cond ((< n 2) 0) (else (* (A232748 n) (- (A232748 n) (A232748 (- n 1)))))))
%Y A232749 A005228 gives the positions of zeros.
%Y A232749 Cf. A030124, A232747, A232748, A232751.
%K A232749 nonn
%O A232749 1,4
%A A232749 _Antti Karttunen_, Nov 30 2013