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a(0)=1; thereafter a(n) = smallest number missing from A081145 after A081145(n) has been calculated.
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%I #11 May 17 2019 08:14:43

%S 1,2,3,3,3,5,5,5,6,6,6,9,9,9,10,10,10,11,11,11,13,13,13,15,15,15,17,

%T 17,17,18,18,18,19,19,19,22,22,22,23,23,24,24,24,26,26,26,29,29,29,30,

%U 30,30,31,31,31,32,32,32,35,35,35,36,36,36,38,38,38,39,39,39,40,40,43

%N a(0)=1; thereafter a(n) = smallest number missing from A081145 after A081145(n) has been calculated.

%C More than the usual number of terms are shown in order to emphasize the irregularities.

%C Usually the terms appear in groups of three, but there are many irregularities. To see them, take this sequence, apply the RUNS transform twice, and bisect the result. This produces a very irregular sequence, 12, 10, 1, 46, 2, 2, 3, 2, 5, 6, 7, 10, 9, 13, 25, 5, 24, 1, 42, ... It would be nice to understand this better.

%H Rémy Sigrist, <a href="/A308172/b308172.txt">Table of n, a(n) for n = 0..25000</a>

%H Rémy Sigrist, <a href="/A308172/a308172.gp.txt">PARI program for A308172</a>

%e n=4: Terms 1 through 4 of A081145 are 1,2,4,7. After A081145(4)=7 has been calculated, the numbers not yet in A081145 are 3,5,6,8,..., so a(4) = 3.

%o (PARI) See Links section.

%Y Cf. A081145.

%K nonn

%O 0,2

%A _N. J. A. Sloane_, May 16 2019