A051466 Largest product of primorials less than A025487(n) that divides A025487(n).

1, 2, 2, 4, 6, 8, 12, 6, 16, 12, 24, 30, 32, 36, 48, 60, 64, 72, 60, 96, 30, 72, 120, 128, 144, 180, 192, 210, 216, 240, 256, 288, 360, 384, 420, 432, 180, 480, 512, 360, 576, 420, 432, 720, 768, 840, 864, 900, 960, 1024, 1080, 1152, 210, 1260, 1296, 1440

Offset

2,2

Comments

Note that A036041(A025487(n)) = A036041(a(n)) + 1 since A025487(n)/a(n) is prime.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 2..10000

Formula

a(n) = A025487(n) / p, where p is the largest prime such that p^A051282(n) | A025487(n). - Charlie Neder, Oct 12 2018

Example

A025487 = 1, 2, 4, 6, 8, 12, 16, 24, 30, 32, 36, ...; a(n)= 1, 2, 2, 4, 6, 8, 12, 6, 16, 12, ... . (12 divides 36, but 16 through 32 do not.)
A025487(38) = 900 = 5#*5#. The largest product of primorials that divides this number will be 5#*3# = 180 = a(38). - Charlie Neder, Oct 20 2018

Mathematica

(* First, load second program at A025487, then: *)
With[{s = Union@ Flatten@ f[5]}, Table[SelectFirst[Reverse@ Take[s, n - 1], Mod[s[[n]], #] == 0 &], {n, 2, Length@ s}]] (* Michael De Vlieger, Dec 27 2019 *)

Prog

(Haskell)
a051466 n = a051466_list !! (n-2)
a051466_list = f [head a025487_list] $ tail a025487_list where
   f us (v:vs) = fromJust (find (\x -> mod v x == 0) us) : f (v : us) vs
-- Reinhard Zumkeller, Jul 17 2013

Crossrefs

Cf. A036041, A034776.

Sequence in context: A361394 A147982 A329899 * A320193 A260215 A261156

Adjacent sequences: A051463 A051464 A051465 * A051467 A051468 A051469

Keyword

easy,nice,nonn

Author

Alford Arnold

Extensions

Offset updated by Matthew Vandermast, Jul 03 2012

Name edited by Charlie Neder, Oct 20 2018

Name clarified by Antti Karttunen, Dec 24 2019

Status

approved