21997756561523 has 4 divisors (see below), whose sum is σ = 22048795440288. Its totient is φ = 21946717682760.

The previous prime is 21997756561519. The next prime is 21997756561531. The reversal of 21997756561523 is 32516565779912.

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

It is a cyclic number.

It is not a de Polignac number, because 21997756561523 - 2² = 21997756561519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21997756561423) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 25519438736 + ... + 25519439597.

It is an arithmetic number, because the mean of its divisors is an integer number (5512198860072).

Almost surely, 2^{21997756561523} is an apocalyptic number.

21997756561523 is a deficient number, since it is larger than the sum of its proper divisors (51038878765).

21997756561523 is an equidigital number, since it uses as much as digits as its factorization.

21997756561523 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51038878764.

The product of its digits is 214326000, while the sum is 68.

The spelling of 21997756561523 in words is "twenty-one trillion, nine hundred ninety-seven billion, seven hundred fifty-six million, five hundred sixty-one thousand, five hundred twenty-three".