1811079

Appears in sequences

• Cubeful "year numbers" (such that phi(n) = 2 phi(sigma(n)): A137815).at n=3A137817
• Non-biquadratefree "year numbers": phi(n) = 2 phi(sigma(n)) and p^4 | n for some p>1.at n=1A137818
• Year numbers, i.e., phi(n) = 2 phi(sigma(n)), divisible by a 5th prime power.at n=0A137819