21043653121 has 4 divisors (see below), whose sum is σ = 21058589700. Its totient is φ = 21028716544.

The previous prime is 21043653109. The next prime is 21043653131. The reversal of 21043653121 is 12135634012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1349460225 + 19694192896 = 36735^2 + 140336^2 .

It is a cyclic number.

It is not a de Polignac number, because 21043653121 - 2¹⁹ = 21043128833 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21043653121.

It is not an unprimeable number, because it can be changed into a prime (21043653131) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7466176 + ... + 7468993.

It is an arithmetic number, because the mean of its divisors is an integer number (5264647425).

Almost surely, 2^21043653121 is an apocalyptic number.

It is an amenable number.

21043653121 is a deficient number, since it is larger than the sum of its proper divisors (14936579).

21043653121 is a wasteful number, since it uses less digits than its factorization.

21043653121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14936578.

The product of its (nonzero) digits is 4320, while the sum is 28.

The spelling of 21043653121 in words is "twenty-one billion, forty-three million, six hundred fifty-three thousand, one hundred twenty-one".