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A351870 a(n) is the least k such that A351868(k) = n.

%I A351870 #6 Feb 25 2022 10:57:24
%S A351870 0,1,2,3,4,5,6,7,8,9,10,11111111111,12,13,14,15,16,17,18,19,20,21,112,
%T A351870 23,24,25,26,27,28,29,30,31,32,1113,34,35,36,37,38,39,40,41,42,43,224,
%U A351870 45,46,47,48,49,50,51,52,53,54,111115,56,57,58,59,60,61,62
%N A351870 a(n) is the least k such that A351868(k) = n.
%H A351870 Rémy Sigrist, <a href="/A351870/a351870.gp.txt">PARI program</a>
%F A351870 a(n) <= A002275(n).
%e A351870 For n = 44:
%e A351870 - the number 44 could encode 1 or 2 runs of consecutive equal digits,
%e A351870 - for 1 run, we have the following possibilities:
%e A351870        11111111111111111111111111111111111111111111 (44 1's)
%e A351870        2222222222222222222222 (22 2's)
%e A351870        44444444444 (11 4's)
%e A351870 - for 2 runs, we have the following possibilities:
%e A351870        11114 (4 1's and then 1 4's)
%e A351870        224 (2 2's and then 1 4's)
%e A351870        111122 (4 1's and then 2 2's)
%e A351870        422 (1 4's and then 2 2's)
%e A351870        221111 (2 2's and then 4 1's)
%e A351870        41111 (1 4's and then 4 1's)
%e A351870 - the least possibility is 224,
%e A351870 - so a(44) = 224.
%o A351870 (PARI) See Links section.
%Y A351870 Cf. A002275, A351868.
%K A351870 nonn,base
%O A351870 0,3
%A A351870 _Rémy Sigrist_, Feb 22 2022