21921291 has 12 divisors (see below), whose sum is σ = 36187632. Its totient is φ = 12526416.

The previous prime is 21921287. The next prime is 21921299. The reversal of 21921291 is 19212912.

It is not a de Polignac number, because 21921291 - 2² = 21921287 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21921299) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 173916 + ... + 174041.

It is an arithmetic number, because the mean of its divisors is an integer number (3015636).

Almost surely, 2^21921291 is an apocalyptic number.

21921291 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21921291 is a deficient number, since it is larger than the sum of its proper divisors (14266341).

21921291 is a wasteful number, since it uses less digits than its factorization.

21921291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 347970 (or 347967 counting only the distinct ones).

The product of its digits is 648, while the sum is 27.

The square root of 21921291 is about 4682.0178342249. The cubic root of 21921291 is about 279.8693735931.

The spelling of 21921291 in words is "twenty-one million, nine hundred twenty-one thousand, two hundred ninety-one".