21215817 has 16 divisors (see below), whose sum is σ = 35921280. Its totient is φ = 12123216.

The previous prime is 21215809. The next prime is 21215827. The reversal of 21215817 is 71851212.

It is not a de Polignac number, because 21215817 - 2³ = 21215809 is a prime.

It is a super-2 number, since 2×21215817² = 900221781954978, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21215807) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 55938 + ... + 56315.

It is an arithmetic number, because the mean of its divisors is an integer number (2245080).

Almost surely, 2^21215817 is an apocalyptic number.

21215817 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21215817 is a deficient number, since it is larger than the sum of its proper divisors (14705463).

21215817 is a wasteful number, since it uses less digits than its factorization.

21215817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 112269 (or 112263 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21215817 is about 4606.0630694770. The cubic root of 21215817 is about 276.8343138058.

The spelling of 21215817 in words is "twenty-one million, two hundred fifteen thousand, eight hundred seventeen".