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A302563
Numbers whose digital root is equal to their number of digits.
0
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
1,2
COMMENTS
Last term is a(111111111) = 999999999. - Giovanni Resta, Aug 16 2018
EXAMPLE
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.
MATHEMATICA
Select[Range[1000], IntegerLength[#] == Mod[#-1, 9] + 1 &] (* Giovanni Resta, Aug 16 2018 *)
PROG
(PARI) isok(n) = if(n, (n-1)%9+1) == #Str(n); \\ Michel Marcus, Aug 16 2018
CROSSREFS
KEYWORD
nonn,easy,fini,base
AUTHOR
Halfdan Skjerning, Aug 16 2018
STATUS
approved