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 A069903 Number of distinct prime factors of n-th triangular number. 6

%I

%S 0,1,2,2,2,2,2,2,2,2,3,3,2,3,3,2,2,2,3,4,3,2,3,3,2,2,3,3,3,3,2,3,3,3,

%T 4,3,2,3,4,3,3,3,3,4,3,2,3,3,2,3,4,3,2,3,4,4,3,2,4,4,2,3,3,3,4,3,3,4,

%U 4,3,3,3,2,3,4,4,4,3,3,3,2,2,4,5,3,3,4,3,3,4

%N Number of distinct prime factors of n-th triangular number.

%C a(n) = A001221(A000217(n)).

%H Harvey P. Dale, <a href="/A069903/b069903.txt">Table of n, a(n) for n = 1..1000</a>

%e A000217(11) = 11*(11+1)/2 = 66 = 2*3*11, therefore a(11) = 3.

%t PrimeNu[#]&/@Accumulate[Range[90]] (* _Harvey P. Dale_, Oct 06 2016 *)

%Y Cf. A069901, A069902, A069904.

%K nonn

%O 1,3

%A _Reinhard Zumkeller_, Apr 10, 2002

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Last modified May 31 02:51 EDT 2020. Contains 334747 sequences. (Running on oeis4.)