20991005 has 16 divisors (see below), whose sum is σ = 30481920. Its totient is φ = 13546752.

The previous prime is 20991001. The next prime is 20991007. The reversal of 20991005 is 50019902.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 20991005 - 2² = 20991001 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20991001) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17045 + ... + 18234.

It is an arithmetic number, because the mean of its divisors is an integer number (1905120).

Almost surely, 2^20991005 is an apocalyptic number.

It is an amenable number.

20991005 is a deficient number, since it is larger than the sum of its proper divisors (9490915).

20991005 is a wasteful number, since it uses less digits than its factorization.

20991005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35308.

The product of its (nonzero) digits is 810, while the sum is 26.

The square root of 20991005 is about 4581.5941548767. The cubic root of 20991005 is about 275.8530207063.

The spelling of 20991005 in words is "twenty million, nine hundred ninety-one thousand, five".