21256106391 has 24 divisors (see below), whose sum is σ = 33256213536. Its totient is φ = 13005057600.

The previous prime is 21256106387. The next prime is 21256106413. The reversal of 21256106391 is 19360165212.

21256106391 is a `hidden beast` number, since 2 + 1 + 2 + 5 + 6 + 10 + 639 + 1 = 666.

It is not a de Polignac number, because 21256106391 - 2² = 21256106387 is a prime.

It is a super-2 number, since 2×21256106391² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256106491) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 504835 + ... + 545316.

It is an arithmetic number, because the mean of its divisors is an integer number (1385675564).

Almost surely, 2^21256106391 is an apocalyptic number.

21256106391 is a deficient number, since it is larger than the sum of its proper divisors (12000107145).

21256106391 is a wasteful number, since it uses less digits than its factorization.

21256106391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1050343 (or 1050340 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The spelling of 21256106391 in words is "twenty-one billion, two hundred fifty-six million, one hundred six thousand, three hundred ninety-one".