20640690 has 128 divisors (see below), whose sum is σ = 64235520. Its totient is φ = 4618944.

The previous prime is 20640679. The next prime is 20640713. The reversal of 20640690 is 9604602.

It is a super-2 number, since 2×20640690² = 852076167352200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 126549 + ... + 126711.

It is an arithmetic number, because the mean of its divisors is an integer number (501840).

Almost surely, 2^20640690 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20640690, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32117760).

20640690 is an abundant number, since it is smaller than the sum of its proper divisors (43594830).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20640690 is a wasteful number, since it uses less digits than its factorization.

20640690 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 253 (or 247 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 27.

The square root of 20640690 is about 4543.2026148962. The cubic root of 20640690 is about 274.3098506941.

The spelling of 20640690 in words is "twenty million, six hundred forty thousand, six hundred ninety".