OFFSET
2,1
LINKS
Indranil Ghosh, Table of n, a(n) for n = 2..10000
FORMULA
EXAMPLE
For n = 10, sigma(10) = 18 and the sum of the prime factors of 18 is 2 + 3 = 5. So, a(10) = 5. - Indranil Ghosh, Jan 13 2017
MATHEMATICA
Table[Apply[Plus, Transpose[FactorInteger[DivisorSigma[1, n]]][[1]]], {n, 3, 100}]
PROG
(Python)
from sympy import isprime
def sigma(n):
return sum(i for i in range(1, n+1) if n % i == 0)
def sopf(n):
return sum(i for i in range(1, n+1) if n % i == 0 and isprime(i))
def A080649(n):
return sopf(sigma(n))
for i in range(2, 101):
print(str(i)+" "+str(A080649(i))) # Indranil Ghosh, Jan 15 2017
(PARI) a(n) = vecsum(factor(sigma(n))[, 1]); \\ Michel Marcus, Jan 14 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Joseph L. Pe, Feb 28 2003
STATUS
approved