21271691 has 4 divisors (see below), whose sum is σ = 24310512. Its totient is φ = 18232872.

The previous prime is 21271667. The next prime is 21271699. The reversal of 21271691 is 19617212.

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

It is not a de Polignac number, because 21271691 - 2¹⁴ = 21255307 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21271699) 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, 1519400 + ... + 1519413.

It is an arithmetic number, because the mean of its divisors is an integer number (6077628).

Almost surely, 2^21271691 is an apocalyptic number.

21271691 is a deficient number, since it is larger than the sum of its proper divisors (3038821).

21271691 is an equidigital number, since it uses as much as digits as its factorization.

21271691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3038820.

The product of its digits is 1512, while the sum is 29.

The square root of 21271691 is about 4612.1243478467. The cubic root of 21271691 is about 277.0771244970.

The spelling of 21271691 in words is "twenty-one million, two hundred seventy-one thousand, six hundred ninety-one".