21991347 has 36 divisors (see below), whose sum is σ = 37773216. Its totient is φ = 12287520.

The previous prime is 21991313. The next prime is 21991349. The reversal of 21991347 is 74319912.

It is not a de Polignac number, because 21991347 - 2⁷ = 21991219 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21991349) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 20197 + ... + 21257.

It is an arithmetic number, because the mean of its divisors is an integer number (1049256).

Almost surely, 2^21991347 is an apocalyptic number.

21991347 is a deficient number, since it is larger than the sum of its proper divisors (15781869).

21991347 is a wasteful number, since it uses less digits than its factorization.

21991347 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1128 (or 1118 counting only the distinct ones).

The product of its digits is 13608, while the sum is 36.

The square root of 21991347 is about 4689.4932562058. The cubic root of 21991347 is about 280.1671918143.

The spelling of 21991347 in words is "twenty-one million, nine hundred ninety-one thousand, three hundred forty-seven".