21291081 has 16 divisors (see below), whose sum is σ = 32572800. Its totient is φ = 12117888.

The previous prime is 21291029. The next prime is 21291091. The reversal of 21291081 is 18019212.

It is not a de Polignac number, because 21291081 - 2⁹ = 21290569 is a prime.

It is a super-2 number, since 2×21291081² = 906620260297122, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21291091) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3765 + ... + 7533.

It is an arithmetic number, because the mean of its divisors is an integer number (2035800).

Almost surely, 2^21291081 is an apocalyptic number.

21291081 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21291081 is a deficient number, since it is larger than the sum of its proper divisors (11281719).

21291081 is a wasteful number, since it uses less digits than its factorization.

21291081 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4048.

The product of its (nonzero) digits is 288, while the sum is 24.

The square root of 21291081 is about 4614.2259372510. The cubic root of 21291081 is about 277.1612879022.

The spelling of 21291081 in words is "twenty-one million, two hundred ninety-one thousand, eighty-one".