A022512 Describe previous term from the right (method A - initial term is 8).

8, 18, 1811, 211811, 21182112, 122112182112, 122112181112212211, 2122112231181112212211, 21221122311821132221221112, 12312211321321121821132221221112

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy
• nice

Comments

Method A = 'frequency' followed by 'digit'-indication.

Examples

			E.g., the term after 1811 is obtained by saying "two 1's, one 8, one 1", which gives 211811.
		

Crossrefs

Cf. A022506, A006711, A022482, A022507-A022513.

Programs

Mathematica

split[n_]:=Split[Reverse[IntegerDigits[n]]];
list1[n_]:=List/@Length/@split[n];riffle1[n_]:=Riffle[split[n],list1[n]];
tab[n_]:=Table[i,{i,1,2*Length[list1[n]],2}];
list2[n_]:=Append[riffle1[n][[#]],riffle1[n][[#+1]]]&/@tab[n];
flat[n_]:=Flatten/@list2[n];riffle2[n_]:=Riffle[Last/@flat[n],First/@flat[n]];
a[1]=8; a[n_]:=FromDigits[riffle2[a[n-1]]]; Array[a,10] (* or *)
IntegerReverse[NestList[FromDigits[Flatten[Replace[Replace[Replace[Split[Reverse[IntegerDigits[#]]],{x_,y_}->{x,Length[{x,y}]},{1}],{x_,y_,z_}->{x,Length[{x,y,z}]},{1}],{x_}->{x,Length[{x}]},{1}]]]&,8,9]] (* Ivan N. Ianakiev, Nov 10 2016 *)

Extensions

More terms from Erich Friedman