21351640 has 32 divisors (see below), whose sum is σ = 48545280. Its totient is φ = 8451072.

The previous prime is 21351637. The next prime is 21351661. The reversal of 21351640 is 4615312.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1129 + ... + 6631.

It is an arithmetic number, because the mean of its divisors is an integer number (1517040).

Almost surely, 2^21351640 is an apocalyptic number.

21351640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21351640 is an abundant number, since it is smaller than the sum of its proper divisors (27193640).

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

21351640 is a wasteful number, since it uses less digits than its factorization.

21351640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5611 (or 5607 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21351640 is about 4620.7834833500. The cubic root of 21351640 is about 277.4238191446.

Adding to 21351640 its reverse (4615312), we get a palindrome (25966952).

The spelling of 21351640 in words is "twenty-one million, three hundred fifty-one thousand, six hundred forty".