21518641 has 4 divisors (see below), whose sum is σ = 21583984. Its totient is φ = 21453300.

The previous prime is 21518611. The next prime is 21518647. The reversal of 21518641 is 14681512.

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 21518641 - 2²¹ = 19421489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21518647) 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, 32175 + ... + 32836.

It is an arithmetic number, because the mean of its divisors is an integer number (5395996).

Almost surely, 2^21518641 is an apocalyptic number.

It is an amenable number.

21518641 is a deficient number, since it is larger than the sum of its proper divisors (65343).

21518641 is an equidigital number, since it uses as much as digits as its factorization.

21518641 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65342.

The product of its digits is 1920, while the sum is 28.

The square root of 21518641 is about 4638.8189229587. The cubic root of 21518641 is about 278.1452280200.

The spelling of 21518641 in words is "twenty-one million, five hundred eighteen thousand, six hundred forty-one".