A260521 Concatenate the positions of digits 9, 8,..., 0 in the decimal representation of n, using 1 for the rightmost digit etc., and 0 when the digit does not occur.

1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 21, 120, 120, 1020, 10020, 100020, 1000020, 10000020, 100000020, 1000000020, 201, 210, 1200, 1200, 10200, 100200, 1000200, 10000200, 100000200, 1000000200

Offset: 0

Author

M. F. Hasler, Jul 28 2015

Keywords

• nonn
• base

Examples

			Consider n=1103, digits '9' through '4' do not occur, digit '3' at 1st position (looking from the right), digit '2' does not occur, digit '1' in 3rd and 4th place, and digit '0' is at 2nd position. Thus a(1103) = 00000010342 = 10342.
		

Crossrefs

Cf. A045918 (the classical "look and say" sequence).

Cf. A260519 - A260522 for variants (counting from the right or starting with digit 0).

Programs

PARI

A260521=a(n)={my(p=vector(10));for(i=1,#n=if(n,Vecrev(digits(n)),[0]),p[n[i]+1]=if(p[n[i]+1],concat(p[n[i]+1],i),i));p=concat(Vecrev(p));p[1]=Str(p[1]);eval(concat(p))}