OFFSET
1,1
EXAMPLE
For n=4, a = <2,3,5>, yielding sums <1+2*3*5, 2+3*5, 2*3+5, 2*3*5+1> = <31,17,11,31>, with least prime factor a(4)=11.
PROG
(PARI) prodsum(ls) = local(left=1, right=prod(x=1, #ls, ls[x]), o=vector(#ls)); for(x=1, #ls, left*=ls[x]; right/=ls[x]; o[x]=left+right); o
newlpf(v) = local(l=0, fs); for(x=1, #v, fs=factor(v[x], if(l>500000, 0, l)); if(!l||fs[1, 1]<l, l=fs[1, 1])); l
s=[2]; while(#s<80, s=concat(s, [newlpf(prodsum(s))]))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Phil Carmody, Feb 23 2013
STATUS
approved