21621431 has 16 divisors (see below), whose sum is σ = 24259200. Its totient is φ = 19139328.

The previous prime is 21621427. The next prime is 21621437. The reversal of 21621431 is 13412612.

It is not a de Polignac number, because 21621431 - 2² = 21621427 is a prime.

It is a super-2 number, since 2×21621431² = 934972556975522, 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 (21621437) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37715 + ... + 38283.

It is an arithmetic number, because the mean of its divisors is an integer number (1516200).

Almost surely, 2^21621431 is an apocalyptic number.

21621431 is a deficient number, since it is larger than the sum of its proper divisors (2637769).

21621431 is a wasteful number, since it uses less digits than its factorization.

21621431 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 698.

The product of its digits is 288, while the sum is 20.

The square root of 21621431 is about 4649.8850523427. The cubic root of 21621431 is about 278.5874050259.

The spelling of 21621431 in words is "twenty-one million, six hundred twenty-one thousand, four hundred thirty-one".