3999137

Appears in sequences

• Numbers k such that 2^sigma(k) == -1 (mod k).at n=6A276238
• Numbers k such that 2^psi(k) == -1 (mod k) where psi(k) = A001615(k).at n=21A291164
• Numbers m that divide 4^(m + 1) + 1.at n=6A329168