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A118668
Number of distinct digits needed to write the n-th triangular number in decimal representation.
9
1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 1, 1, 2, 2, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 3, 1, 3, 3, 3, 3, 3, 3, 3, 2, 4, 3, 3, 3, 3, 4, 4, 4, 3, 4, 4, 4, 4, 2, 3, 4, 3, 4, 4, 3, 4, 2, 3, 4, 4, 4, 3, 3, 4, 3, 4, 3, 2, 4, 4, 4, 3, 3, 4, 4, 3, 4, 3, 4, 3, 4, 4, 4, 4, 3, 4, 3, 4, 4, 4, 2, 2, 3, 3, 4
OFFSET
0,5
COMMENTS
0 < a(n) <= 10;
a(n) = A043537(A000217(n)).
LINKS
EXAMPLE
n=99: 99*(99+1)/2 = 4950 -> a(99) = #{0,4,5,9} = 4;
see A119033 for an overview of sequences with terms composed of not more than 3 distinct digits.
n=100: 100*(100+1)/2 = 5050 -> a(100) = #{0,5} = 2;
MATHEMATICA
Length[Union[IntegerDigits[#]]]&/@Accumulate[Range[0, 110]] (* Harvey P. Dale, Jul 23 2012 *)
PROG
(Haskell)
a118668 = a043537 . a000217
a118668_list = map a043537 a000217_list
-- Reinhard Zumkeller, Jul 11 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Reinhard Zumkeller, May 19 2006
STATUS
approved