A298972 Number of positive integers k < n such that n occurs in the Reverse-and-Add trajectory of k.

0, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 2, 2, 0, 1, 0, 4, 0, 1, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0

Offset: 0

Author

Felix Fröhlich, Jan 30 2018

Keywords

• nonn
• base

Comments

Number of integers k < n such that n occurs in row k of A243238.

For n > 0, a(n) = 0 iff n is a term of A067031.

For n > 0, a(n) > 0 iff n is a term of A067030.

Examples

			For n = 22: There exist 4 positive integers k < 22 such that 22 occurs in the Reverse-and-Add trajectory of k, namely 5, 10, 11 and 20, so a(22) = 4.
		

Links

• Index entries for sequences related to Reverse and Add!

Crossrefs

Cf. A056964, A067030, A067031, A243238.

Programs

Mathematica

Block[{nn = 85, s}, s = Array[Union@ NestWhileList[# + IntegerReverse@ # &, #, # < nn &, 1, nn] &, nn]; Array[Count[Take[s, # - 1], #, 2] &, nn + 1, 0]] (* Michael De Vlieger, Feb 01 2018 *)

PARI

a(n) = my(i=0); for(k=1, n-1, my(x=k); while(x < n, x=x+eval(concat(Vecrev(Str(x))))); if(x==n, i++)); i