21087261 has 12 divisors (see below), whose sum is σ = 32802588. Its totient is φ = 12976704.

The previous prime is 21087221. The next prime is 21087277. The reversal of 21087261 is 16278012.

It can be written as a sum of positive squares in 2 ways, for example, as 6502500 + 14584761 = 2550^2 + 3819^2 .

It is not a de Polignac number, because 21087261 - 2⁶ = 21087197 is a prime.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21087211) 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, 90000 + ... + 90233.

It is an arithmetic number, because the mean of its divisors is an integer number (2733549).

Almost surely, 2^21087261 is an apocalyptic number.

It is an amenable number.

21087261 is a deficient number, since it is larger than the sum of its proper divisors (11715327).

21087261 is a wasteful number, since it uses less digits than its factorization.

21087261 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180252 (or 180249 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21087261 is about 4592.0867805389. The cubic root of 21087261 is about 276.2740268340.

Subtracting from 21087261 its reverse (16278012), we obtain a square (4809249 = 2193²).

The spelling of 21087261 in words is "twenty-one million, eighty-seven thousand, two hundred sixty-one".