20398640 has 80 divisors (see below), whose sum is σ = 51344928. Its totient is φ = 7507968.

The previous prime is 20398627. The next prime is 20398643. The reversal of 20398640 is 4689302.

It is a tau number, because it is divible by the number of its divisors (80).

It is a super-2 number, since 2×20398640² = 832209027699200, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 20398597 and 20398606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20398643) 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, 71939 + ... + 72221.

Almost surely, 2^20398640 is an apocalyptic number.

20398640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20398640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25672464).

20398640 is an abundant number, since it is smaller than the sum of its proper divisors (30946288).

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

20398640 is a wasteful number, since it uses less digits than its factorization.

20398640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 366 (or 360 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 32.

The square root of 20398640 is about 4516.4853592146. The cubic root of 20398640 is about 273.2333694869.

The spelling of 20398640 in words is "twenty million, three hundred ninety-eight thousand, six hundred forty".