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.

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

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: A371349 A013581 A350536 * A057909 A228916 A345431

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