21581091 has 24 divisors (see below), whose sum is σ = 35748960. Its totient is φ = 12289536.

The previous prime is 21581083. The next prime is 21581099. The reversal of 21581091 is 19018512.

It is an interprime number because it is at equal distance from previous prime (21581083) and next prime (21581099).

It is not a de Polignac number, because 21581091 - 2³ = 21581083 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21581099) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 31731 + ... + 32403.

It is an arithmetic number, because the mean of its divisors is an integer number (1489540).

Almost surely, 2^21581091 is an apocalyptic number.

21581091 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21581091 is a deficient number, since it is larger than the sum of its proper divisors (14167869).

21581091 is a wasteful number, since it uses less digits than its factorization.

21581091 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1195 (or 1192 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 21581091 is about 4645.5452855397. The cubic root of 21581091 is about 278.4140398067.

It can be divided in two parts, 2158 and 1091, that added together give a square (3249 = 57²).

The spelling of 21581091 in words is "twenty-one million, five hundred eighty-one thousand, ninety-one".