A133996 a(n) = the smallest positive integer with exactly n positive "non-isolated divisors". A divisor, k, of n is non-isolated if (k-1) or (k+1) also divides n.

2, 6, 12, 30, 60, 90, 180, 360, 630, 420, 840, 1680, 4200, 1260, 2520, 3780, 7560, 15120, 13860, 36960, 49140, 27720, 32760, 65520, 83160, 98280, 196560, 314160, 277200, 491400, 526680, 471240, 360360, 1164240, 942480, 720720, 1081080

Offset

2,1

Links

Ray Chandler, Table of n, a(n) for n=2..85

Mathematica

With[{s = KeySort@ PositionIndex@ Table[1 + Count[Rest@ Divisors@ n, _?(AnyTrue[# + {-1, 1}, Divisible[n, #] &] &)], {n, 1200000}]}, Function[t, TakeWhile[#, # > 0 &] &@ Rest@ ReplacePart[t, Map[# -> Lookup[s, #][[1]] &, Keys@ s]]]@ ConstantArray[0, Last@ Keys@ s]] (* Michael De Vlieger, Oct 11 2017 *)

Crossrefs

Cf. A133997, A132747.

Sequence in context: A038199 A056267 A348412 * A284573 A355475 A080742

Adjacent sequences: A133993 A133994 A133995 * A133997 A133998 A133999

Keyword

nonn

Author

Leroy Quet, Oct 01 2007

Extensions

Extended by Ray Chandler, Jun 24 2008

Status

approved