OFFSET
1,1
COMMENTS
Alladi and Erdős ask if this sequence is infinite and give 3 terms: 2*3*5, 2*3*5*7*11*13*17*19 and 2*3*5*7*11*13*17*19*23*29*31*37*41, that is, a(1), a(4) and a(12).
This sequence contains A159578(n) for all values of n > 1. - Altug Alkan, Jan 07 2016
LINKS
Hiroaki Yamanouchi, Table of n, a(n) for n = 1..500
K. Alladi and P. Erdős, On an additive arithmetic function, Pacific J. Math., Volume 71, Number 2 (1977), 275-294.
PROG
(PARI) sopfr(n) = {my(f=factor(n)); sum(k=1, #f~, f[k, 1]*f[k, 2]); }
list(lim)= {my(v=List(), p, t); for(e=2, log(lim+.5)\log(2), p=1; t=prod(i=1, e-1, prime(i)); forprime(q=prime(e), lim, t*=q/p; if(t>lim, next(2)); if (! (t % sopfr(t)), listput(v, t)); p=nextprime(p+1))); vecsort(Vec(v)); } \\ adapted from A097889
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Jan 07 2016
EXTENSIONS
a(13)-a(17) from Hiroaki Yamanouchi, Jan 12 2016
STATUS
approved