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A165497 a(n) starts arithmetic progression of n terms separated by tau(a(n)), each term having the same number of divisors 2
1, 3, 3, 60, 60, 201, 481, 5989, 3122037, 4434429, 13576837, 183894465, 187925171, 209072257, 1498642520, 12239200420, 20220712468, 20220712468, 875023683404, 992997544772, 2721798771116, 9770941874212, 9770941874212 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(15) > 10^9.

a(19) > 10^11. - Donovan Johnson, Sep 24 2009

a(24) > 10^13. - Giovanni Resta, Aug 02 2013

LINKS

Table of n, a(n) for n=1..23.

EXAMPLE

tau(60) = tau(72) = tau(84) = tau(96) = tau(108) = 12. This is the first such progression of length greater than 3, so a(4) and a(5) are both 60.

PROG

(PARI) has(n)=my(t=numdiv(n), s=1); while(numdiv(n+=t)==t, s++); s

a(n)=my(k); while(has(k++)<n, ); k \\ Charles R Greathouse IV, Apr 24 2015

CROSSREFS

Cf. A064491, A165498, A165499.

Sequence in context: A290567 A100065 A066807 * A051752 A102065 A102074

Adjacent sequences:  A165494 A165495 A165496 * A165498 A165499 A165500

KEYWORD

hard,nonn,more

AUTHOR

Hugo van der Sanden, Sep 21 2009

EXTENSIONS

a(15)-a(18) from Donovan Johnson, Sep 24 2009

a(19)-a(23) from Giovanni Resta, Aug 02 2013

STATUS

approved

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Last modified November 18 10:18 EST 2017. Contains 294887 sequences.