21515971 has 8 divisors (see below), whose sum is σ = 22546944. Its totient is φ = 20493000.

The previous prime is 21515957. The next prime is 21515983. The reversal of 21515971 is 17951512.

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

It is not a de Polignac number, because 21515971 - 2⁷ = 21515843 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21515171) 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 7 ways as a sum of consecutive naturals, for example, 3910 + ... + 7636.

It is an arithmetic number, because the mean of its divisors is an integer number (2818368).

Almost surely, 2^21515971 is an apocalyptic number.

21515971 is a deficient number, since it is larger than the sum of its proper divisors (1030973).

21515971 is a wasteful number, since it uses less digits than its factorization.

21515971 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4001.

The product of its digits is 3150, while the sum is 31.

The square root of 21515971 is about 4638.5311252594. The cubic root of 21515971 is about 278.1337235996.

The spelling of 21515971 in words is "twenty-one million, five hundred fifteen thousand, nine hundred seventy-one".