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A232749
Inverse function to Hofstadter's A030124.
5
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, 23, 24, 25, 26, 27, 28, 0, 29, 30, 31, 32, 33, 34, 35, 36, 37, 0, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 0, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 0, 60
OFFSET
1,4
COMMENTS
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.
Note that A232747(n)*a(n) = 0 for all n.
Used to compute the permutation A232751.
MATHEMATICA
nmax = 100; A5228 = {1};
Module[{d = 2, k = 1}, Do[While[MemberQ[A5228, d], d++];
k += d; d++; AppendTo[A5228, k], {n, 1, nmax}]];
a46[n_] := For[k = 1, True, k++, If[A5228[[k]] > n, Return[k - 1]]];
a48[n_] := a48[n] = If[n == 1, 0, a48[n-1] + (1 - (a46[n] - a46[n - 1]))];
a[n_] := If[n == 1, 0, a48[n] (a48[n] - a48[n - 1])];
Array[a, nmax] (* Jean-François Alcover, Dec 09 2021 *)
PROG
(Scheme, with memoization macro definec from Antti Karttunen's IntSeq-library)
(definec (A232749 n) (cond ((< n 2) 0) (else (* (A232748 n) (- (A232748 n) (A232748 (- n 1)))))))
CROSSREFS
A005228 gives the positions of zeros.
Sequence in context: A119974 A195828 A322981 * A181578 A065332 A265515
KEYWORD
nonn
AUTHOR
Antti Karttunen, Nov 30 2013
STATUS
approved