21993534821 has 2 divisors, whose sum is σ = 21993534822. Its totient is φ = 21993534820.

The previous prime is 21993534781. The next prime is 21993534833. The reversal of 21993534821 is 12843539912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21983992900 + 9541921 = 148270^2 + 3089^2 .

It is a cyclic number.

It is not a de Polignac number, because 21993534821 - 2¹⁰ = 21993533797 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21993524821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10996767410 + 10996767411.

It is an arithmetic number, because the mean of its divisors is an integer number (10996767411).

Almost surely, 2^21993534821 is an apocalyptic number.

It is an amenable number.

21993534821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21993534821 is an equidigital number, since it uses as much as digits as its factorization.

21993534821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 466560, while the sum is 47.

The spelling of 21993534821 in words is "twenty-one billion, nine hundred ninety-three million, five hundred thirty-four thousand, eight hundred twenty-one".