21927982561 has 9 divisors (see below), whose sum is σ = 22042450521. Its totient is φ = 21814108272.

The previous prime is 21927982553. The next prime is 21927982589. The reversal of 21927982561 is 16528972912.

The square root of 21927982561 is 148081.

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

It can be written as a sum of positive squares in 4 ways, for example, as 1018822561 + 20909160000 = 31919^2 + 144600^2 .

It is not a de Polignac number, because 21927982561 - 2³ = 21927982553 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21927982499 and 21927982508.

It is not an unprimeable number, because it can be changed into a prime (21927982511) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 55234015 + ... + 55234411.

It is an arithmetic number, because the mean of its divisors is an integer number (2449161169).

Almost surely, 2^21927982561 is an apocalyptic number.

21927982561 is the 148081-st square number.

21927982561 is the 74041-st centered octagonal number.

It is an amenable number.

21927982561 is a deficient number, since it is larger than the sum of its proper divisors (114467960).

21927982561 is an frugal number, since it uses more digits than its factorization.

21927982561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1540 (or 770 counting only the distinct ones).

The product of its digits is 1088640, while the sum is 52.

The spelling of 21927982561 in words is "twenty-one billion, nine hundred twenty-seven million, nine hundred eighty-two thousand, five hundred sixty-one".