OFFSET
1,1
COMMENTS
It is easy to see that if f(n) = A024919(n) = Sum_{k=1..n} (-1)^k*k*floor(n/k) then f(n) = f(n-1) + (2^(L+1)-3)*sigma(M) if n=2^L*M, where M is odd and L >= 0. Using this we can get a faster program to calculate this sequence. - Robert Gerbicz, Aug 30 2002
MATHEMATICA
f[n_] := Sum[(-1)^i*i*Floor[n/i], {i, 1, n}]; Do[s = f[n]; If[s == 0, Print[n]], {n, 1, 40000}]
PROG
(PARI) lista(nn) = {my(s=-1); for(m=2, nn, x=bitand(m, -m); if((s+=(2*x-3)*sigma(m/x)) == 0, print1(m, ", "))); } \\ Jinyuan Wang, Apr 06 2020
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Benoit Cloitre, Aug 10 2002
EXTENSIONS
Four more terms from Klaus Brockhaus, Aug 13 2002
More terms from Robert Gerbicz, Aug 30 2002
a(14) from Giovanni Resta, Apr 06 2020
STATUS
approved