A260522 Concatenate the positions of digits 9, 8,..., 0 in the decimal representation of n, using 1 for the leftmost digit etc., and 0 when the digit does not occur.

1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000, 12, 120, 210, 2010, 20010, 200010, 2000010, 20000010, 200000010, 2000000010, 102, 120, 1200, 2100, 20100, 200100, 2000100, 20000100, 200000100, 2000000100

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 4th position, digit '2' does not occur, digit '1' in 1st and 2nd place, and digit '0' is at 3rd position. Thus a(1103) = 00000040123 = 40123.
		

Crossrefs

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

Cf. A260519 - A260521 for variants (counting from the right or starting with digit 0).

Programs

PARI

a(n)={my(p=vector(10));for(i=1,#n=if(n,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))}