21256042163391 has 24 divisors (see below), whose sum is σ = 35137605461504. Its totient is φ = 12129602340240.

The previous prime is 21256042163381. The next prime is 21256042163393. The reversal of 21256042163391 is 19336124065212.

21256042163391 is a `hidden beast` number, since 2 + 1 + 2 + 5 + 6 + 0 + 4 + 2 + 1 + 633 + 9 + 1 = 666.

It is not a de Polignac number, because 21256042163391 - 2⁹ = 21256042162879 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21256042163393) 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, 232001995 + ... + 232093596.

Almost surely, 2^{21256042163391} is an apocalyptic number.

21256042163391 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21256042163391 is a deficient number, since it is larger than the sum of its proper divisors (13881563298113).

21256042163391 is a wasteful number, since it uses less digits than its factorization.

21256042163391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 464096331 (or 464096328 counting only the distinct ones).

The product of its (nonzero) digits is 466560, while the sum is 45.

The spelling of 21256042163391 in words is "twenty-one trillion, two hundred fifty-six billion, forty-two million, one hundred sixty-three thousand, three hundred ninety-one".