21542643 has 6 divisors (see below), whose sum is σ = 31117164. Its totient is φ = 14361756.

The previous prime is 21542639. The next prime is 21542663. The reversal of 21542643 is 34624512.

21542643 is a `hidden beast` number, since 2 + 15 + 4 + 2 + 643 = 666.

It is not a de Polignac number, because 21542643 - 2² = 21542639 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21542623) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1196805 + ... + 1196822.

It is an arithmetic number, because the mean of its divisors is an integer number (5186194).

Almost surely, 2^21542643 is an apocalyptic number.

21542643 is a deficient number, since it is larger than the sum of its proper divisors (9574521).

21542643 is a wasteful number, since it uses less digits than its factorization.

21542643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2393633 (or 2393630 counting only the distinct ones).

The product of its digits is 5760, while the sum is 27.

The square root of 21542643 is about 4641.4052828858. The cubic root of 21542643 is about 278.2486044544.

The spelling of 21542643 in words is "twenty-one million, five hundred forty-two thousand, six hundred forty-three".