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A289838 a(n) = A289815(n) * A289816(n). 3
1, 2, 2, 3, 6, 6, 3, 6, 6, 4, 10, 10, 12, 30, 30, 12, 30, 30, 4, 10, 10, 12, 30, 30, 12, 30, 30, 5, 14, 14, 15, 42, 42, 15, 42, 42, 20, 70, 70, 60, 210, 210, 60, 210, 210, 20, 70, 70, 60, 210, 210, 60, 210, 210, 5, 14, 14, 15, 42, 42, 15, 42, 42, 20, 70, 70 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Each number k > 0 appears 2^omega(k) times (where omega = A001221).

a(A004488(n)) = a(n) for any n >= 0.

The number of distinct prime factors of a(n) equals the number of nonzero digits in the ternary representation of n.

LINKS

Rémy Sigrist, Table of n, a(n) for n = 0..10000

EXAMPLE

a(42) = A289815(42) * A289816(42) = 20 * 3 = 60.

PROG

(PARI) a(n) = my (v=1);                        \

       for (o=2, oo,                           \

           if (n==0, return (v));              \

           if (gcd(v, o)==1 && omega(o)==1,    \

               if (n % 3, v *= o);             \

               n \= 3;                         \

           );                                  \

       );

(Python)

from sympy import floor, gcd, primefactors

def omega(n): return 0 if n==1 else len(primefactors(n))

def a(n):

    v, o = 1, 2

    while True:

        if n==0: return v

        if gcd(v, o)==1 and omega(o)==1:

            if n%3: v*=o

            n=floor(n/3)

        o+=1

print map(a, xrange(101)) # Indranil Ghosh, Aug 02 2017

CROSSREFS

Cf. A001221, A004488, A289815, A289816.

Sequence in context: A308483 A070871 A096115 * A290734 A093919 A179661

Adjacent sequences:  A289835 A289836 A289837 * A289839 A289840 A289841

KEYWORD

nonn,base,look

AUTHOR

Rémy Sigrist, Jul 13 2017

STATUS

approved

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Last modified October 21 20:44 EDT 2019. Contains 328315 sequences. (Running on oeis4.)