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A072486 a(1) = 1, a(n) = a(n-1) times smallest prime factor of n. 6
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = 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

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Last modified October 19 09:28 EDT 2018. Contains 316339 sequences. (Running on oeis4.)