21731643 has 24 divisors (see below), whose sum is σ = 33106320. Its totient is φ = 13715520.

The previous prime is 21731623. The next prime is 21731653. The reversal of 21731643 is 34613712.

21731643 is a `hidden beast` number, since 2 + 17 + 3 + 1 + 643 = 666.

It is not a de Polignac number, because 21731643 - 2⁶ = 21731579 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21731623) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 13048 + ... + 14618.

It is an arithmetic number, because the mean of its divisors is an integer number (1379430).

Almost surely, 2^21731643 is an apocalyptic number.

21731643 is a deficient number, since it is larger than the sum of its proper divisors (11374677).

21731643 is a wasteful number, since it uses less digits than its factorization.

21731643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1659 (or 1656 counting only the distinct ones).

The product of its digits is 3024, while the sum is 27.

The square root of 21731643 is about 4661.7210341246. The cubic root of 21731643 is about 279.0599555121.

The spelling of 21731643 in words is "twenty-one million, seven hundred thirty-one thousand, six hundred forty-three".