OFFSET
1,2
LINKS
Zak Seidov, Table of n, a(n) for n = 1..1000
FORMULA
EXAMPLE
105 = 3 * 5 * 7 is a squarefree triangular number.
MAPLE
# uses code of A000217
isA061304 := proc(n)
isA000217(n) and issqrfree(n) ;
simplify(%) ;
end proc:
for n from 1 to 5000 do
if isA061304(n) then
printf("%d, ", n);
end if;
end do: # R. J. Mathar, Oct 05 2017
MATHEMATICA
Select[Accumulate[Range[0, 100]], SquareFreeQ] (* Jean-François Alcover, Apr 17 2020 *)
PROG
(PARI) isA078779F(f)=for(i=2, #f~, if(f[i, 2]>1, return(0))); #f~==0 || f[1, 2]==1 || (f[1, 2]==2 && f[1, 1]==2)
list(lim)=my(v=List(), ok=1); forfactored(n=2, (sqrtint(lim\1*8+1)+1)\2, e=n[2][, 2]; if(isA078779F(n[2]), if(ok, listput(v, binomial(n[1], 2)), ok=1), ok=0)); Vec(v) \\ Charles R Greathouse IV, Nov 05 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amarnath Murthy, Apr 26 2001
STATUS
approved