login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A133997 a(n) = the smallest positive integer with exactly n positive "isolated divisors". A divisor, k, of n is isolated if neither (k-1) nor (k+1) divides n. 3
1, 3, 9, 15, 36, 45, 126, 96, 144, 120, 324, 240, 336, 432, 360, 480, 672, 864, 720, 840, 1260, 1008, 1080, 1920, 1440, 2040, 1680, 2016, 2160, 3024, 2880, 2520, 4620, 4200, 3360, 5544, 4320, 6048, 6300, 9072, 7200, 11700, 5040, 12096, 7920, 7560, 10800 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Ray Chandler, Table of n, a(n) for n=1..577

MATHEMATICA

With[{s = KeySort@ PositionIndex@ Table[1 + Count[Rest@ Divisors@ n, _?(NoneTrue[# + {-1, 1}, Divisible[n, #] &] &)], {n, 12000}]}, Function[t, TakeWhile[#, # > 0 &] &@ ReplacePart[t, Map[# -> Lookup[s, #][[1]] &, Keys@ s]]]@ ConstantArray[0, Last@ Keys@ s]] (* Michael De Vlieger, Oct 11 2017 *)

CROSSREFS

Cf. A133996, A132881.

Sequence in context: A031159 A058039 A013581 * A057909 A228916 A082702

Adjacent sequences:  A133994 A133995 A133996 * A133998 A133999 A134000

KEYWORD

nonn

AUTHOR

Leroy Quet, Oct 01 2007

EXTENSIONS

Extended by Ray Chandler, Jun 24 2008

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 18 02:19 EDT 2020. Contains 337164 sequences. (Running on oeis4.)