Are All Perfect Numbers Even?/Progress/Prime Factors/Historical Note

Historical Note on Prime Factors of Odd Perfect Number
published a proof in $1973$ that an odd perfect number $P$ has the properties that:
 * either:
 * at least one of the prime powers factoring $P$ is greater than $10^{18}$
 * the power of such a prime factor is even
 * or:
 * there is no divisor of $P$ less than $7$.

published a proof in $1980$ that an odd perfect number has at least $8$ distinct prime factors.

and published a proof in $1998$ that an odd perfect number has at least one prime factor which is greater than $1 \, 000 \, 000$.