21255666731 has 4 divisors (see below), whose sum is σ = 22890718032. Its totient is φ = 19620615432.

The previous prime is 21255666721. The next prime is 21255666769. The reversal of 21255666731 is 13766655212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21255666731 is a prime.

It is a super-2 number, since 2×21255666731² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21255666721) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 817525631 + ... + 817525656.

It is an arithmetic number, because the mean of its divisors is an integer number (5722679508).

Almost surely, 2^21255666731 is an apocalyptic number.

21255666731 is a deficient number, since it is larger than the sum of its proper divisors (1635051301).

21255666731 is a wasteful number, since it uses less digits than its factorization.

21255666731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1635051300.

The product of its digits is 453600, while the sum is 44.

The spelling of 21255666731 in words is "twenty-one billion, two hundred fifty-five million, six hundred sixty-six thousand, seven hundred thirty-one".