21720551765 has 32 divisors (see below), whose sum is σ = 30340828800. Its totient is φ = 14760299520.

The previous prime is 21720551761. The next prime is 21720551807. The reversal of 21720551765 is 56715502712.

It is a happy number.

It is not a de Polignac number, because 21720551765 - 2² = 21720551761 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720551761) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 66080 + ... + 218649.

It is an arithmetic number, because the mean of its divisors is an integer number (948150900).

Almost surely, 2^21720551765 is an apocalyptic number.

It is an amenable number.

21720551765 is a deficient number, since it is larger than the sum of its proper divisors (8620277035).

21720551765 is a wasteful number, since it uses less digits than its factorization.

21720551765 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 284837.

The product of its (nonzero) digits is 147000, while the sum is 41.

The spelling of 21720551765 in words is "twenty-one billion, seven hundred twenty million, five hundred fifty-one thousand, seven hundred sixty-five".