OFFSET

1,2

COMMENTS

MATHEMATICA

s[n_] := If[n == 1, {1}, s[n] = Join[s[n-1], Length /@ Split[s[n-1]]]];

a[n_] := FromDigits[s[n]];

Array[a, 9] (* Jean-François Alcover, Feb 24 2021 *)

CROSSREFS

KEYWORD

nonn,base

AUTHOR

N. J. A. Sloane, Jan 31 2019

STATUS

approved