21542991 has 16 divisors (see below), whose sum is σ = 29634528. Its totient is φ = 13910400.

The previous prime is 21542977. The next prime is 21542993. The reversal of 21542991 is 19924512.

It is not a de Polignac number, because 21542991 - 2⁵ = 21542959 is a prime.

It is a super-2 number, since 2×21542991² = 928200922452162, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21542993) 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, 46501 + ... + 46961.

It is an arithmetic number, because the mean of its divisors is an integer number (1852158).

Almost surely, 2^21542991 is an apocalyptic number.

21542991 is a deficient number, since it is larger than the sum of its proper divisors (8091537).

21542991 is a wasteful number, since it uses less digits than its factorization.

21542991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 922.

The product of its digits is 6480, while the sum is 33.

The square root of 21542991 is about 4641.4427713805. The cubic root of 21542991 is about 278.2501027229.

The spelling of 21542991 in words is "twenty-one million, five hundred forty-two thousand, nine hundred ninety-one".