21871509 has 8 divisors (see below), whose sum is σ = 31813152. Its totient is φ = 13255440.

The previous prime is 21871453. The next prime is 21871519. The reversal of 21871509 is 90517812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21871509 - 2⁸ = 21871253 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33), and also a Moran number because the ratio is a prime number: 662773 = 21871509 / (2 + 1 + 8 + 7 + 1 + 5 + 0 + 9).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21871509.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21871519) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 331354 + ... + 331419.

It is an arithmetic number, because the mean of its divisors is an integer number (3976644).

Almost surely, 2^21871509 is an apocalyptic number.

It is an amenable number.

21871509 is a deficient number, since it is larger than the sum of its proper divisors (9941643).

21871509 is a wasteful number, since it uses less digits than its factorization.

21871509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 662787.

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21871509 is about 4676.6985149783. The cubic root of 21871509 is about 279.6573572313.

The spelling of 21871509 in words is "twenty-one million, eight hundred seventy-one thousand, five hundred nine".