21618401 has 4 divisors (see below), whose sum is σ = 24706752. Its totient is φ = 18530052.

The previous prime is 21618383. The next prime is 21618403. The reversal of 21618401 is 10481612.

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 21618401 - 2¹⁰ = 21617377 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21618403) 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, 1544165 + ... + 1544178.

It is an arithmetic number, because the mean of its divisors is an integer number (6176688).

Almost surely, 2^21618401 is an apocalyptic number.

It is an amenable number.

21618401 is a deficient number, since it is larger than the sum of its proper divisors (3088351).

21618401 is an equidigital number, since it uses as much as digits as its factorization.

21618401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3088350.

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 21618401 is about 4649.5592264214. The cubic root of 21618401 is about 278.5743907891.

The spelling of 21618401 in words is "twenty-one million, six hundred eighteen thousand, four hundred one".