21642989821 has 2 divisors, whose sum is σ = 21642989822. Its totient is φ = 21642989820.

The previous prime is 21642989789. The next prime is 21642989897. The reversal of 21642989821 is 12898924612.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20566428100 + 1076561721 = 143410^2 + 32811^2 .

It is a cyclic number.

It is not a de Polignac number, because 21642989821 - 2⁵ = 21642989789 is a prime.

It is a super-2 number, since 2×21642989821² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21642983821) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10821494910 + 10821494911.

It is an arithmetic number, because the mean of its divisors is an integer number (10821494911).

Almost surely, 2^21642989821 is an apocalyptic number.

It is an amenable number.

21642989821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21642989821 is an equidigital number, since it uses as much as digits as its factorization.

21642989821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 995328, while the sum is 52.

The spelling of 21642989821 in words is "twenty-one billion, six hundred forty-two million, nine hundred eighty-nine thousand, eight hundred twenty-one".