21291243 has 16 divisors (see below), whose sum is σ = 29519616. Its totient is φ = 13638240.

The previous prime is 21291239. The next prime is 21291247. The reversal of 21291243 is 34219212.

It is an interprime number because it is at equal distance from previous prime (21291239) and next prime (21291247).

It is not a de Polignac number, because 21291243 - 2² = 21291239 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21291247) 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, 8058 + ... + 10368.

It is an arithmetic number, because the mean of its divisors is an integer number (1844976).

Almost surely, 2^21291243 is an apocalyptic number.

21291243 is a deficient number, since it is larger than the sum of its proper divisors (8228373).

21291243 is a wasteful number, since it uses less digits than its factorization.

21291243 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2434.

The product of its digits is 864, while the sum is 24.

The square root of 21291243 is about 4614.2434916246. The cubic root of 21291243 is about 277.1619908572.

The spelling of 21291243 in words is "twenty-one million, two hundred ninety-one thousand, two hundred forty-three".