21132991 has 4 divisors (see below), whose sum is σ = 23054184. Its totient is φ = 19211800.

The previous prime is 21132983. The next prime is 21133003. The reversal of 21132991 is 19923112.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21132991 - 2³ = 21132983 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21132931) 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, 960580 + ... + 960601.

It is an arithmetic number, because the mean of its divisors is an integer number (5763546).

Almost surely, 2^21132991 is an apocalyptic number.

21132991 is a deficient number, since it is larger than the sum of its proper divisors (1921193).

21132991 is a wasteful number, since it uses less digits than its factorization.

21132991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1921192.

The product of its digits is 972, while the sum is 28.

The square root of 21132991 is about 4597.0633017177. The cubic root of 21132991 is about 276.4735926524.

The spelling of 21132991 in words is "twenty-one million, one hundred thirty-two thousand, nine hundred ninety-one".