OFFSET
1,1
LINKS
R. J. Mathar, Table of n, a(n) for n = 1..10491
Henry Ibstedt, Surfing on the Ocean of Numbers, Erhus Univ. Press, Vail, 1997.
FORMULA
Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = zeta(2) * (zeta(2) * zeta(5) * Product_{p prime} (1-1/p^2+1/p^3-1/p^4) - 1)/(zeta(2)-1)^2 = 0.6611256641303... . - Amiram Eldar, Jan 06 2024
MAPLE
isA013929 := proc(n)
not numtheory[issqrfree](n) ;
end proc:
A013929 := proc(n)
option remember;
local a;
if n = 1 then
4;
else
for a from procname(n-1)+1 do
if isA013929(a) then
return a;
end if;
end do:
end if;
end proc:
A015050 := proc(n)
local m ;
m := A013929(n) ;
for k from 1 do
if modp(k^3, m) = 0 then
return k;
end if;
end do:
end proc:
MATHEMATICA
f[p_, e_] := p^Ceiling[e/3]; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; s /@ Select[Range[200], !SquareFreeQ[#] &] (* Amiram Eldar, Feb 09 2021 *)
PROG
(PARI) lista(kmax) = {my(f); for(k = 2, kmax, f = factor(k); if(!issquarefree(f), print1(prod(i = 1, #f~, f[i, 1]^ceil(f[i, 2]/3)), ", "))); } \\ Amiram Eldar, Jan 06 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
R. Muller
EXTENSIONS
Description corrected by Diego Torres (torresvillarroel(AT)hotmail.com), Jun 23 2002
STATUS
approved