21056517 has 20 divisors (see below), whose sum is σ = 32129856. Its totient is φ = 13736520.

The previous prime is 21056507. The next prime is 21056527. The reversal of 21056517 is 71565012.

21056517 is a `hidden beast` number, since 2 + 1 + 0 + 5 + 651 + 7 = 666.

It is an interprime number because it is at equal distance from previous prime (21056507) and next prime (21056527).

It is not a de Polignac number, because 21056517 - 2⁴ = 21056501 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21056507) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 1042 + ... + 6572.

Almost surely, 2^21056517 is an apocalyptic number.

21056517 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21056517 is a deficient number, since it is larger than the sum of its proper divisors (11073339).

21056517 is an equidigital number, since it uses as much as digits as its factorization.

21056517 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5590 (or 5581 counting only the distinct ones).

The product of its (nonzero) digits is 2100, while the sum is 27.

The square root of 21056517 is about 4588.7380618205. The cubic root of 21056517 is about 276.1396977109.

The spelling of 21056517 in words is "twenty-one million, fifty-six thousand, five hundred seventeen".