21591441 has 20 divisors (see below), whose sum is σ = 32488500. Its totient is φ = 14289696.

The previous prime is 21591433. The next prime is 21591443. The reversal of 21591441 is 14419512.

21591441 is a `hidden beast` number, since 215 + 9 + 1 + 441 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 12006225 + 9585216 = 3465^2 + 3096^2 .

It is not a de Polignac number, because 21591441 - 2³ = 21591433 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21591443) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 11175 + ... + 12963.

It is an arithmetic number, because the mean of its divisors is an integer number (1624425).

Almost surely, 2^21591441 is an apocalyptic number.

It is an amenable number.

21591441 is a deficient number, since it is larger than the sum of its proper divisors (10897059).

21591441 is a wasteful number, since it uses less digits than its factorization.

21591441 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1950 (or 1941 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21591441 is about 4646.6591224233. The cubic root of 21591441 is about 278.4585405656.

It can be divided in two parts, 2159 and 1441, that added together give a square (3600 = 60²).

The spelling of 21591441 in words is "twenty-one million, five hundred ninety-one thousand, four hundred forty-one".