21640481 has 4 divisors (see below), whose sum is σ = 22143792. Its totient is φ = 21137172.

The previous prime is 21640477. The next prime is 21640499. The reversal of 21640481 is 18404612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21640481 - 2² = 21640477 is a prime.

It is a super-2 number, since 2×21640481² = 936620835822722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21640481.

It is not an unprimeable number, because it can be changed into a prime (21640441) 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, 251591 + ... + 251676.

It is an arithmetic number, because the mean of its divisors is an integer number (5535948).

Almost surely, 2^21640481 is an apocalyptic number.

It is an amenable number.

21640481 is a deficient number, since it is larger than the sum of its proper divisors (503311).

21640481 is an equidigital number, since it uses as much as digits as its factorization.

21640481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 503310.

The product of its (nonzero) digits is 1536, while the sum is 26.

The square root of 21640481 is about 4651.9330390710. The cubic root of 21640481 is about 278.6691993683.

The spelling of 21640481 in words is "twenty-one million, six hundred forty thousand, four hundred eighty-one".