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A138221 a(n) = the smallest divisor of n that is >= the number of positive divisors of n. 3
1, 2, 3, 4, 5, 6, 7, 4, 3, 5, 11, 6, 13, 7, 5, 8, 17, 6, 19, 10, 7, 11, 23, 8, 5, 13, 9, 7, 29, 10, 31, 8, 11, 17, 5, 9, 37, 19, 13, 8, 41, 14, 43, 11, 9, 23, 47, 12, 7, 10, 17, 13, 53, 9, 5, 8, 19, 29, 59, 12, 61, 31, 7, 8, 5, 11, 67, 17, 23, 10, 71, 12, 73, 37, 15, 19, 7, 13, 79, 10, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..81.

FORMULA

a(n) = n for all primes plus the integers {1, 4, 6}. - Robert G. Wilson v

EXAMPLE

There are four positive divisors of 15: (1,3,5,15). The smallest of these divisors that is >=4 is 5; so a(15) = 5.

MAPLE

with(numtheory): a:=proc(n) local dn, i: dn:=divisors(n): for i while dn[i] < tau(n) do end do: dn[i] end proc: seq(a(n), n=1..60); # Emeric Deutsch, Mar 17 2008

MATHEMATICA

f[n_] := First@Select[Divisors@n, # >= DivisorSigma[0, n] &]; Array[f, 81] (* Robert G. Wilson v *)

CROSSREFS

Cf. A138222, A138223, A138224, A000005.

Sequence in context: A245347 A278059 A115871 * A038388 A272573 A319999

Adjacent sequences:  A138218 A138219 A138220 * A138222 A138223 A138224

KEYWORD

nonn

AUTHOR

Leroy Quet, Mar 06 2008

EXTENSIONS

More terms from Emeric Deutsch, Robert G. Wilson v and Erich Friedman, Mar 17 2008

STATUS

approved

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Last modified March 25 01:17 EDT 2019. Contains 321450 sequences. (Running on oeis4.)