21491137 has 4 divisors (see below), whose sum is σ = 21504816. Its totient is φ = 21477460.

The previous prime is 21491101. The next prime is 21491149. The reversal of 21491137 is 73119412.

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 21491137 - 2¹⁹ = 20966849 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21491237) 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, 4123 + ... + 7744.

It is an arithmetic number, because the mean of its divisors is an integer number (5376204).

Almost surely, 2^21491137 is an apocalyptic number.

It is an amenable number.

21491137 is a deficient number, since it is larger than the sum of its proper divisors (13679).

21491137 is a wasteful number, since it uses less digits than its factorization.

21491137 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13678.

The product of its digits is 1512, while the sum is 28.

The square root of 21491137 is about 4635.8534273637. The cubic root of 21491137 is about 278.0266739411.

The spelling of 21491137 in words is "twenty-one million, four hundred ninety-one thousand, one hundred thirty-seven".