21309901 has 4 divisors (see below), whose sum is σ = 21472704. Its totient is φ = 21147100.

The previous prime is 21309877. The next prime is 21309907. The reversal of 21309901 is 10990312.

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 21309901 - 2¹⁹ = 20785613 is a prime.

It is a super-2 number, since 2×21309901² = 908223761259602, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21309907) 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, 81205 + ... + 81466.

It is an arithmetic number, because the mean of its divisors is an integer number (5368176).

Almost surely, 2^21309901 is an apocalyptic number.

It is an amenable number.

21309901 is a deficient number, since it is larger than the sum of its proper divisors (162803).

21309901 is a wasteful number, since it uses less digits than its factorization.

21309901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 162802.

The product of its (nonzero) digits is 486, while the sum is 25.

The square root of 21309901 is about 4616.2648320910. The cubic root of 21309901 is about 277.2429283360.

The spelling of 21309901 in words is "twenty-one million, three hundred nine thousand, nine hundred one".