A302563 Numbers whose digital root is equal to their number of digits.

1, 11, 20, 29, 38, 47, 56, 65, 74, 83, 92, 102, 111, 120, 129, 138, 147, 156, 165, 174, 183, 192, 201, 210, 219, 228, 237, 246, 255, 264, 273, 282, 291, 300, 309, 318, 327, 336, 345, 354, 363, 372, 381, 390, 399, 408, 417, 426, 435, 444

Offset: 1

Author

Halfdan Skjerning, Aug 16 2018

Keywords

• nonn
• easy
• fini
• base

Comments

Last term is a(111111111) = 999999999. - Giovanni Resta, Aug 16 2018

Examples

			11 and 111 belong to the set as they both have the same number of digits as their digital root, respectively; 11 has two digits and also digital root two, and 111 has three digits and digital root three. 302563 does not belong to the set, since it has six digits and digital root one.
		

Crossrefs

Cf. A010888, A055642, A098955.

Programs

Mathematica

Select[Range[1000], IntegerLength[#] == Mod[#-1, 9] + 1 &] (* Giovanni Resta, Aug 16 2018 *)

PARI

isok(n) = if(n, (n-1)%9+1) == #Str(n); \\ Michel Marcus, Aug 16 2018