A072486 a(1) = 1, a(n) = a(n-1) times smallest prime factor of n.

1, 2, 6, 12, 60, 120, 840, 1680, 5040, 10080, 110880, 221760, 2882880, 5765760, 17297280, 34594560, 588107520, 1176215040, 22348085760, 44696171520, 134088514560, 268177029120, 6168071669760, 12336143339520, 61680716697600

Offset

1,2

Comments

a(n) is the product of the smallest divisors > 1 of all the numbers from 2 to n.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Example

a(5) = 60. a(6) = 1*2*3*2*5*2 = 120. Also a(6) = a(5) * 2 = 120.

Mathematica

a = {1}; Do[AppendTo[a, a[[n - 1]] FactorInteger[n][[1, 1]]], {n, 2, 25}]; a (* Michael De Vlieger, Aug 25 2015 *)
nxt[{n_, a_}]:={n+1, a*FactorInteger[n+1][[1, 1]]}; NestList[nxt, {1, 1}, 30][[All, 2]] (* Harvey P. Dale, May 03 2018 *)

Prog

(PARI) al(n)=local(v=vector(n)); v[1]=1; for(k=2, n, v[k]=v[k-1]*factor(k)[1, 1]); v  \\ Franklin T. Adams-Watters, Jan 13 2012
(PARI) A072486(n)=prod(k=2, n, factor(k)[1, 1])  \\ M. F. Hasler, Jan 13 2012
(Haskell)
a072486 n = a072486_list !! (n-1)
a072486_list = scanl1 (*) a020639_list
-- Reinhard Zumkeller, Apr 10 2014

Crossrefs

Cf. A020639, A104350.

Sequence in context: A135060 A185021 A191836 * A096123 A081125 A138570

Adjacent sequences: A072483 A072484 A072485 * A072487 A072488 A072489

Keyword

nonn

Author

Amarnath Murthy, Jul 13 2002

Extensions

More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 25 2003

Status

approved