21871815 has 32 divisors (see below), whose sum is σ = 40604160. Its totient is φ = 9846144.

The previous prime is 21871807. The next prime is 21871841. The reversal of 21871815 is 51817812.

It is not a de Polignac number, because 21871815 - 2³ = 21871807 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5481 + ... + 8589.

It is an arithmetic number, because the mean of its divisors is an integer number (1268880).

Almost surely, 2^21871815 is an apocalyptic number.

21871815 is a deficient number, since it is larger than the sum of its proper divisors (18732345).

21871815 is a wasteful number, since it uses less digits than its factorization.

21871815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3191.

The product of its digits is 4480, while the sum is 33.

The square root of 21871815 is about 4676.7312302505. The cubic root of 21871815 is about 279.6586614357.

It can be divided in two parts, 2187181 and 5, that added together give a triangular number (2187186 = T₂₀₉₁).

The spelling of 21871815 in words is "twenty-one million, eight hundred seventy-one thousand, eight hundred fifteen".