21006657 has 12 divisors (see below), whose sum is σ = 34677760. Its totient is φ = 12003768.

The previous prime is 21006641. The next prime is 21006673. The reversal of 21006657 is 75660012.

21006657 is a `hidden beast` number, since 2 + 1 + 0 + 0 + 6 + 657 = 666.

It is an interprime number because it is at equal distance from previous prime (21006641) and next prime (21006673).

It is not a de Polignac number, because 21006657 - 2⁴ = 21006641 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21006657.

It is not an unprimeable number, because it can be changed into a prime (21006607) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 166657 + ... + 166782.

Almost surely, 2^21006657 is an apocalyptic number.

It is an amenable number.

21006657 is a deficient number, since it is larger than the sum of its proper divisors (13671103).

21006657 is a wasteful number, since it uses less digits than its factorization.

21006657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333452 (or 333449 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 27.

The square root of 21006657 is about 4583.3019756503. The cubic root of 21006657 is about 275.9215671903.

Adding to 21006657 its reverse (75660012), we get a palindrome (96666669).

The spelling of 21006657 in words is "twenty-one million, six thousand, six hundred fifty-seven".