OFFSET
1,2
COMMENTS
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Paul Pollack and Carl Pomerance, Some problems of Erdős on the sum-of-divisors function, For Richard Guy on his 99th birthday: May his sequence be unbounded, Trans. Amer. Math. Soc. Ser. B 3 (2016), 1-26.
FORMULA
A001065(a(n)) <= a(n). - Reinhard Zumkeller, Oct 31 2015
MAPLE
isA263837 := proc(n)
if 2*n-numtheory[sigma](n) >=0 then
true;
else
false;
end if;
end proc:
A263837 := proc(n)
option remember;
local a;
if n =1 then
1;
else
for a from procname(n-1)+1 do
if isA263837(a) then
return a;
end if;
end do:
end if;
end proc:
seq(A263837(n), n=1..100) ; # R. J. Mathar, Jun 06 2024
MATHEMATICA
Select[Range[100], DivisorSigma[1, #] <= 2*# &] (* Amiram Eldar, Mar 14 2024 *)
PROG
(Haskell)
a263837 n = a263837_list !! (n-1)
a263837_list = filter (\x -> a001065 x <= x) [1..]
-- Reinhard Zumkeller, Oct 31 2015
(PARI) isok(n) = sigma(n) <= 2*n; \\ Michel Marcus, Dec 27 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Oct 30 2015
EXTENSIONS
Additional description to the definition added by Antti Karttunen, Aug 28 2020
STATUS
approved