%I #19 Aug 16 2019 16:26:16
%S 35,34,33,36,32,15,15,30,35,25,37,33,15,38,25,17,31,35,24,35,15,16,36,
%T 16,15,29,41,27,16,6,26,38,15,32,16,37,28,20,23,22,36,25,16,16,16,22,
%U 16,18,21,24,33,17,29,37,22,16,17,10,6,17,18,31,41,28,15,17,30,8,40,15
%N Using the mapping in A306979, the sum of powers of 2 where the exponents are the digits of the previous term, a(n) is the number of steps to reach the end of the first cycle.
%C There are only four eventual cycles as cited in A306979:
%C - (148, 274) (length = 2);
%C - (98, 768, 448, 288, 516) (length = 5);
%C - (70, 129, 518, 290, 517, 162) (length = 6);
%C - (5, 32, 12, 6, 64, 80, 257, 164, 82, 260, 69, 576, 224, 24, 20) (length = 15).
%C First occurrence of length k or -1 if no such length occurs for k=2,3,4,...: 148, 184, 1578, 98, 29, 126, 67, 106, 57, 299, 2399, -1, -1, 5, 21, 15, 47, 136, 37, 48, 39, 38, 18, 9, 30, 27, 36, 25, 7, 16, 4, 2, 1, 0, 3, 10, 13, 203, 68, 26, 134, 127, 2357, ..., .
%e a(0) = 35 since the mapping as described in A306979 is that sequence's first 35 terms;
%e a(1) = 34 since it is the sequence above less the first term;
%e a(2) = 33 since it is the sequence above less the first two terms;
%e a(29) = 6 since the sequence is {29 -> 516 -> 98 -> 768 -> 448 -> 288 -> 516 -> ...};
%e a(184) = 3 since the sequence is {184 -> 274 -> 148 -> 274}; etc.
%t g[n_] := Plus @@ (2^IntegerDigits@ n); f[n_] := Length[ NestWhileList[ g@# &, n, UnsameQ, All]] - 1; Array[f, 70, 0]
%Y Cf. A306979.
%K nonn,base
%O 0,1
%A _Jianing Song_ and _Robert G. Wilson v_, Apr 11 2019