OFFSET
1,1
COMMENTS
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
C. K. Caldwell, The Prime Glossary, Number of divisors
P. A. MacMahon, Divisors of numbers and their continuations in the theory of partitions, Proc. London Math. Soc., 19 (1919), 75-113.
Wacław Sierpiński, Number Of Divisors And Their Sum, Elementary theory of numbers, Warszawa, 1964.
EXAMPLE
sigma(2) = 3, tau(3) = 2 and sopf(2) = 2 sigma(2254) = 4104, tau(4104) = 32 and sopf(2254) = 32.
MAPLE
with(numtheory): for n from 1 to 12000 do : t1:= ifactors(n)[2] : t2 :=sum(t1[i][1], i=1..nops(t1)): if tau(sigma(n)) = t2 then print (n): else fi : od :
MATHEMATICA
Select[Range[2, 5100], DivisorSigma[0, DivisorSigma[1, #]]==Total[ FactorInteger[ #][[All, 1]]]&] (* Harvey P. Dale, May 31 2019 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Feb 16 2010
STATUS
approved