21945111762721 has 27 divisors (see below), whose sum is σ = 25651523430963. Its totient is φ = 18719505756000.

The previous prime is 21945111762697. The next prime is 21945111762733. The reversal of 21945111762721 is 12726711154912.

The square root of 21945111762721 is 4684561.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 11804453649121 + 10140658113600 = 3435761^2 + 3184440^2 .

It is not a de Polignac number, because 21945111762721 - 2²⁷ = 21944977544993 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (49).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21945111762221) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 7312598221 + ... + 7312601221.

It is an arithmetic number, because the mean of its divisors is an integer number (950056423369).

Almost surely, 2^{21945111762721} is an apocalyptic number.

21945111762721 is the 4684561-st square number.

21945111762721 is the 2342281-st centered octagonal number.

It is an amenable number.

21945111762721 is a deficient number, since it is larger than the sum of its proper divisors (3706411668242).

21945111762721 is an frugal number, since it uses more digits than its factorization.

21945111762721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6462 (or 3231 counting only the distinct ones).

The product of its digits is 423360, while the sum is 49.

21945111762721 divided by its sum of digits (49) gives a square (447859423729 = 669223²).

The spelling of 21945111762721 in words is "twenty-one trillion, nine hundred forty-five billion, one hundred eleven million, seven hundred sixty-two thousand, seven hundred twenty-one".