20251640 has 16 divisors (see below), whose sum is σ = 45566280. Its totient is φ = 8100640.

The previous prime is 20251631. The next prime is 20251643. The reversal of 20251640 is 4615202.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20251643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 253106 + ... + 253185.

Almost surely, 2^20251640 is an apocalyptic number.

20251640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

20251640 is an abundant number, since it is smaller than the sum of its proper divisors (25314640).

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

20251640 is a wasteful number, since it uses less digits than its factorization.

20251640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506302 (or 506298 counting only the distinct ones).

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 20251640 is about 4500.1822185329. The cubic root of 20251640 is about 272.5754469429.

Adding to 20251640 its reverse (4615202), we get a palindrome (24866842).

The spelling of 20251640 in words is "twenty million, two hundred fifty-one thousand, six hundred forty".