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A078545 Largest prime dividing tau(n), the number of divisors of n. 1
2, 2, 3, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 5, 2, 3, 2, 3, 2, 2, 2, 2, 3, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 3, 2, 2, 5, 3, 3, 2, 3, 2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 3, 7, 2, 2, 2, 3, 2, 2, 2, 3, 2, 2, 3, 3, 2, 2, 2, 5, 5, 2, 2, 3, 2, 2, 2, 2, 2, 3, 2, 3, 2, 2, 2, 3, 2, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

From Robert Israel, Dec 04 2016: (Start)

a(n)=2 if and only if every member of the prime signature of n is of the form 2^k-1.

a(m*k) = max(a(m),a(k)) if m and k are coprime.

(End)

LINKS

Robert Israel, Table of n, a(n) for n = 2..10000

FORMULA

a(n) = A006530(A000005(n)).

MAPLE

f:= n -> max(numtheory:-factorset(numtheory:-tau(n))):

map(f, [$2..100]); # Robert Israel, Dec 04 2016

PROG

(PARI) a(n) = vecmax(factor(numdiv(n))[, 1]); \\ Michel Marcus, Dec 05 2016

CROSSREFS

Cf. A000005, A006530, A078542, A078543, A078544, A124010.

Sequence in context: A329614 A134852 A071188 * A163105 A152235 A278966

Adjacent sequences:  A078542 A078543 A078544 * A078546 A078547 A078548

KEYWORD

nonn

AUTHOR

Labos Elemer, Dec 05 2002

EXTENSIONS

a(2)=2 inserted by Robert Israel, Dec 04 2016

STATUS

approved

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Last modified December 10 12:30 EST 2019. Contains 329895 sequences. (Running on oeis4.)