21240291 has 4 divisors (see below), whose sum is σ = 28320392. Its totient is φ = 14160192.

The previous prime is 21240283. The next prime is 21240311. The reversal of 21240291 is 19204212.

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

It is not a de Polignac number, because 21240291 - 2³ = 21240283 is a prime.

It is a super-2 number, since 2×21240291² = 902299923529362, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21240211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3540046 + ... + 3540051.

It is an arithmetic number, because the mean of its divisors is an integer number (7080098).

Almost surely, 2^21240291 is an apocalyptic number.

21240291 is a deficient number, since it is larger than the sum of its proper divisors (7080101).

21240291 is an equidigital number, since it uses as much as digits as its factorization.

21240291 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7080100.

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 21240291 is about 4608.7190194239. The cubic root of 21240291 is about 276.9407224570.

The spelling of 21240291 in words is "twenty-one million, two hundred forty thousand, two hundred ninety-one".