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A140635 Smallest positive integer having the same number of divisors as n. 9
1, 2, 2, 4, 2, 6, 2, 6, 4, 6, 2, 12, 2, 6, 6, 16, 2, 12, 2, 12, 6, 6, 2, 24, 4, 6, 6, 12, 2, 24, 2, 12, 6, 6, 6, 36, 2, 6, 6, 24, 2, 24, 2, 12, 12, 6, 2, 48, 4, 12, 6, 12, 2, 24, 6, 24, 6, 6, 2, 60, 2, 6, 12, 64, 6, 24, 2, 12, 6, 24, 2, 60, 2, 6, 12, 12, 6, 24, 2, 48, 16, 6, 2, 60, 6, 6, 6, 24, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) <= n for all n. Moreover, a(n) = n if and only if n belongs to A005179.

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A005179(A000005(n)).

PROG

(PARI) A140635(n) = { my(nd = numdiv(n)); for (i=1, n, if (numdiv(i) == nd, return (i))); }; \\ After A139770, Antti Karttunen, May 27 2017

(Python)

from sympy import divisor_count as d

def a(n):

    x=d(n)

    m=1

    while True:

        if d(m)==x: return m

        else: m+=1 # Indranil Ghosh, May 27 2017

CROSSREFS

Cf. A000005, A005179, A139770.

Cf. A019505, A138113, A061300 (sequences that can be defined in terms of this sequence).

Sequence in context: A122457 A319410 A139770 * A283465 A283466 A270492

Adjacent sequences:  A140632 A140633 A140634 * A140636 A140637 A140638

KEYWORD

nonn

AUTHOR

Max Alekseyev, May 19 2008

STATUS

approved

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Last modified September 20 08:08 EDT 2019. Contains 327214 sequences. (Running on oeis4.)