21915691 has 6 divisors (see below), whose sum is σ = 25493820. Its totient is φ = 18784836.

The previous prime is 21915679. The next prime is 21915697. The reversal of 21915691 is 19651912.

21915691 = 113² + 114² + ... + 406².

It is a happy number.

It is not a de Polignac number, because 21915691 - 2¹¹ = 21913643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21915697) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 223581 + ... + 223678.

It is an arithmetic number, because the mean of its divisors is an integer number (4248970).

Almost surely, 2^21915691 is an apocalyptic number.

21915691 is a deficient number, since it is larger than the sum of its proper divisors (3578129).

21915691 is an equidigital number, since it uses as much as digits as its factorization.

21915691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447273 (or 447266 counting only the distinct ones).

The product of its digits is 4860, while the sum is 34.

The square root of 21915691 is about 4681.4197632769. The cubic root of 21915691 is about 279.8455398087.

The spelling of 21915691 in words is "twenty-one million, nine hundred fifteen thousand, six hundred ninety-one".