OFFSET
1,1
COMMENTS
EXAMPLE
21 is in the sequence because the prime factors of 21 are {3,7} => s = 1/3 - 2/7, 1/p = 1/21 and s = p = 1/21.
MAPLE
with(numtheory):nn:=1000:
for n from 1 to nn do:
if type(n, prime)=false
then
x:=factorset(n):n0:=nops(x):
s:=sum('i*((-1)^(i+1))/x[i]', 'i'=1..n0):s0:=product('x[i]', 'i'=1..n0):
s2:=s-1/s0:
if s2=0
then
printf(`%d, `, n):
else
fi:
fi:
od:
PROG
(PARI) lista(nn) = {forcomposite(n=2, nn, my(f = factor(n)[, 1]); if (sum(i=1, #f, i*((-1)^(i+1))/f[i]) == prod(i=1, #f, 1/f[i]), print1(n, ", ")); ); } \\ Michel Marcus, Sep 13 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Dec 13 2014
STATUS
approved