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A061283 Smallest number with exactly 2n-1 divisors. 14
1, 4, 16, 64, 36, 1024, 4096, 144, 65536, 262144, 576, 4194304, 1296, 900, 268435456, 1073741824, 9216, 5184, 68719476736, 36864, 1099511627776, 4398046511104, 3600, 70368744177664, 46656, 589824, 4503599627370496, 82944 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

The terms are always squares (because the divisors of a non-square N come in pairs, d and N/d, and so their number is always even - N. J. A. Sloane, Dec 26 2018).

LINKS

T. D. Noe, Table of n, a(n) for n=1..1000 (using A005179)

FORMULA

a(n) = Min{k | A000005(k)=2n-1}.

a(p) = 2^(p-1) for prime p.

EXAMPLE

for n=15, a(n)=144 with 15 divisors: {1,2,3,4,6,8,9,12...}.

CROSSREFS

Cf. A000005, A000290, A005408, A005179, A003680, A016017, A037992, A055079, A048691.

Sequence in context: A162547 A073533 A330689 * A242354 A001264 A307138

Adjacent sequences:  A061280 A061281 A061282 * A061284 A061285 A061286

KEYWORD

nonn

AUTHOR

Labos Elemer, May 22 2001

STATUS

approved

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Last modified January 21 22:47 EST 2020. Contains 331129 sequences. (Running on oeis4.)