21312757 has 4 divisors (see below), whose sum is σ = 21322080. Its totient is φ = 21303436.

The previous prime is 21312751. The next prime is 21312763. The reversal of 21312757 is 75721312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (21312751) and next prime (21312763).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21312757 is a prime.

It is a super-2 number, since 2×21312757² = 908467221882098, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21312751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1368 + ... + 6670.

It is an arithmetic number, because the mean of its divisors is an integer number (5330520).

Almost surely, 2^21312757 is an apocalyptic number.

It is an amenable number.

21312757 is a deficient number, since it is larger than the sum of its proper divisors (9323).

21312757 is an equidigital number, since it uses as much as digits as its factorization.

21312757 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9322.

The product of its digits is 2940, while the sum is 28.

The square root of 21312757 is about 4616.5741627315. The cubic root of 21312757 is about 277.2553133526.

The spelling of 21312757 in words is "twenty-one million, three hundred twelve thousand, seven hundred fifty-seven".