20906991 has 56 divisors (see below), whose sum is σ = 38088864. Its totient is φ = 11197440.

The previous prime is 20906971. The next prime is 20907001. The reversal of 20906991 is 19960902.

It is not a de Polignac number, because 20906991 - 2⁷ = 20906863 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20906971) by changing a digit.

It is a polite number, since it can be written in 55 ways as a sum of consecutive naturals, for example, 86631 + ... + 86871.

Almost surely, 2^20906991 is an apocalyptic number.

20906991 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

20906991 is a deficient number, since it is larger than the sum of its proper divisors (17181873).

20906991 is an equidigital number, since it uses as much as digits as its factorization.

20906991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 283 (or 268 counting only the distinct ones).

The product of its (nonzero) digits is 8748, while the sum is 36.

The square root of 20906991 is about 4572.4163196279. The cubic root of 20906991 is about 275.4845056575.

The spelling of 20906991 in words is "twenty million, nine hundred six thousand, nine hundred ninety-one".