OFFSET
1,1
REFERENCES
József Sándor, Dragoslav S. Mitrinovic, and Borislav Crstici, Handbook of Number Theory I, Springer Science & Business Media, 2005, Chapter III, p. 119, section III.51.
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Wikipedia, Arithmetic number.
FORMULA
A054025(a(n)) > 0. - Reinhard Zumkeller, Jan 06 2012
A245656(a(n)) = 0. - Reinhard Zumkeller, Jul 28 2014
MAPLE
isA049642 := proc(n)
if modp(numtheory[sigma](n), numtheory[tau](n)) = 0 then
false;
else
true;
end if;
end proc:
A049642 := proc(n)
option remember;
if n = 1 then
2;
else
for a from procname(n-1)+1 do
if isA049642(a) then
return a;
end if;
end do:
end if;
end proc: # R. J. Mathar, Oct 26 2015
MATHEMATICA
Select[Range[175], Mod[DivisorSigma[1, #], DivisorSigma[0, #]] > 0 &] (* Jayanta Basu, Mar 28 2013 *)
PROG
(Haskell)
a049642 n = a049642_list !! (n-1)
a049642_list = filter ((== 0) . a245656) [1..]
-- Reinhard Zumkeller, Jan 06 2012
(GAP) a:=Filtered([1..180], n->Sigma(n) mod Tau(n)>0);; Print(a); # Muniru A Asiru, Jan 25 2019
(PARI) is(n) = {my(f = factor(n)); sigma(f) % numdiv(f) > 0; } \\ Amiram Eldar, Apr 25 2024
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved