21051640 has 16 divisors (see below), whose sum is σ = 47366280. Its totient is φ = 8420640.

The previous prime is 21051637. The next prime is 21051643. The reversal of 21051640 is 4615012.

It is an interprime number because it is at equal distance from previous prime (21051637) and next prime (21051643).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 263106 + ... + 263185.

Almost surely, 2^21051640 is an apocalyptic number.

21051640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21051640 is an abundant number, since it is smaller than the sum of its proper divisors (26314640).

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

21051640 is a wasteful number, since it uses less digits than its factorization.

21051640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 526302 (or 526298 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 21051640 is about 4588.2066213282. The cubic root of 21051640 is about 276.1183767221.

Adding to 21051640 its reverse (4615012), we get a palindrome (25666652).

The spelling of 21051640 in words is "twenty-one million, fifty-one thousand, six hundred forty".