A265009 a(1)=3; for n>1, if n is odd a(n) = spf(Product_{k=1..n-1}(a(k))+1) else a(n) = spf(Product_{k=1..n-1}(a(k))-1), where spf is "smallest prime factor".

3, 2, 7, 41, 1723, 5, 14835031, 220078129935929, 241, 23, 79, 101, 23291, 11, 223, 122386298896281959929015788890561251765109069, 38803, 17, 8209, 59, 199, 3340389589, 11527, 13, 47939, 1163, 599, 27198087874669514440553, 181936481, 31, 383, 9623, 739, 33287, 1061, 6493520653, 587, 709, 6548057, 1823, 361789, 20183

Offset

1,1

Links

Table of n, a(n) for n=1..42.

Mathematica

a[1] = 3; a[n_] := a[n] = FactorInteger[ Product[a[k], {k, n - 1}] + If[OddQ@ n, 1, -1]][[1, 1]]; Array[a, {16}] (* Michael De Vlieger, Nov 30 2015 *)

Prog

(PARI) spf(n)=my(f=factor(n)[1, 1]); f
first(m)=my(v=vector(m)); v[1]=3; for(i=2, m,; v[i]=spf((-1)^(i+1)+prod(j=1, i-1, v[j]))); v

Crossrefs

Cf. A000945, A005265.

Sequence in context: A176802 A363400 A230710 * A358656 A021757 A143312

Adjacent sequences: A265006 A265007 A265008 * A265010 A265011 A265012

Keyword

nonn

Author

Anders Hellström, Nov 30 2015

Extensions

a(20)-a(42) from Hans Havermann, Dec 06 2015

Status

approved