21531861 has 24 divisors (see below), whose sum is σ = 33966296. Its totient is φ = 13063680.

The previous prime is 21531827. The next prime is 21531871. The reversal of 21531861 is 16813512.

It can be written as a sum of positive squares in 4 ways, for example, as 463761 + 21068100 = 681^2 + 4590^2 .

It is not a de Polignac number, because 21531861 - 2⁷ = 21531733 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21531821) 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, 7281 + ... + 9801.

Almost surely, 2^21531861 is an apocalyptic number.

It is an amenable number.

21531861 is a deficient number, since it is larger than the sum of its proper divisors (12434435).

21531861 is a wasteful number, since it uses less digits than its factorization.

21531861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2613 (or 2610 counting only the distinct ones).

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

The square root of 21531861 is about 4640.2436358450. The cubic root of 21531861 is about 278.2021759652.

The spelling of 21531861 in words is "twenty-one million, five hundred thirty-one thousand, eight hundred sixty-one".