OFFSET
1,3
FORMULA
a(1)=1; for n > 1, a(n) = (n-1) * Product_{p prime < (n-1)} p. - Pedro Caceres, Mar 12 2018
MATHEMATICA
rad[n_] := Times @@ (First@# & /@ FactorInteger@n); a[n_] := (n -1)rad[a[n -1]]; a[1] = 1; Array[a, 30] (* Robert G. Wilson v, Dec 14 2016 and modified Dec 24 2016 *)
PROG
(PARI) a(n) = if(n==1, 1, (n-1)*prod(k=1, primepi(n-2), prime(k))); \\ Daniel Suteu, Dec 14 2016
(PARI) rad(n) = factorback(factorint(n)[, 1]);
a(n) = if (n==1, 1, (n-1)*rad(a(n-1))); \\ Michel Marcus, Dec 21 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Jan 05 2002
EXTENSIONS
More terms from Michel Marcus, Mar 17 2018
STATUS
approved