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A069903 Number of distinct prime factors of n-th triangular number. 6
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, 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, 4, 3, 3, 3, 2, 3, 4, 4, 4, 3, 3, 3, 2, 2, 4, 5, 3, 3, 4, 3, 3, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
LINKS
FORMULA
a(n) = A001221(A000217(n)).
EXAMPLE
A000217(11) = 11*(11+1)/2 = 66 = 2*3*11, therefore a(11) = 3.
MATHEMATICA
PrimeNu[#]&/@Accumulate[Range[90]] (* Harvey P. Dale, Oct 06 2016 *)
PROG
(PARI) a(n) = omega(n*(n+1)/2); \\ Michel Marcus, Feb 05 2021
CROSSREFS
Sequence in context: A272231 A209253 A165113 * A331003 A086007 A108582
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 10 2002
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)