21965907681 has 27 divisors (see below), whose sum is σ = 32062754451. Its totient is φ = 14491283184.

The previous prime is 21965907653. The next prime is 21965907721. The reversal of 21965907681 is 18670956912.

The square root of 21965907681 is 148209.

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., 5185296081 + 16780611600 = 72009^2 + 129540^2 .

It is not a de Polignac number, because 21965907681 - 2²¹ = 21963810529 is a prime.

It is a super-2 number, since 2×21965907681² (a number of 21 digits) contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21965907631) 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, 56467435 + ... + 56467823.

Almost surely, 2^21965907681 is an apocalyptic number.

21965907681 is the 148209-th square number.

21965907681 is the 74105-th centered octagonal number.

It is an amenable number.

21965907681 is a deficient number, since it is larger than the sum of its proper divisors (10096846770).

21965907681 is an frugal number, since it uses more digits than its factorization.

21965907681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1038 (or 519 counting only the distinct ones).

The product of its (nonzero) digits is 1632960, while the sum is 54.

The spelling of 21965907681 in words is "twenty-one billion, nine hundred sixty-five million, nine hundred seven thousand, six hundred eighty-one".