21221915 has 32 divisors (see below), whose sum is σ = 30433536. Its totient is φ = 14002560.

The previous prime is 21221909. The next prime is 21221923. The reversal of 21221915 is 51912212.

It is a de Polignac number, because none of the positive numbers 2^k-21221915 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 47684 + ... + 48126.

It is an arithmetic number, because the mean of its divisors is an integer number (951048).

Almost surely, 2^21221915 is an apocalyptic number.

21221915 is a deficient number, since it is larger than the sum of its proper divisors (9211621).

21221915 is a wasteful number, since it uses less digits than its factorization.

21221915 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 539.

The product of its digits is 360, while the sum is 23.

The square root of 21221915 is about 4606.7249755113. The cubic root of 21221915 is about 276.8608344897.

The spelling of 21221915 in words is "twenty-one million, two hundred twenty-one thousand, nine hundred fifteen".