21818363821 has 2 divisors, whose sum is σ = 21818363822. Its totient is φ = 21818363820.

The previous prime is 21818363779. The next prime is 21818363837. The reversal of 21818363821 is 12836381812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21811154596 + 7209225 = 147686^2 + 2685^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21818363821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21818363321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10909181910 + 10909181911.

It is an arithmetic number, because the mean of its divisors is an integer number (10909181911).

Almost surely, 2^21818363821 is an apocalyptic number.

It is an amenable number.

21818363821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21818363821 is an equidigital number, since it uses as much as digits as its factorization.

21818363821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 110592, while the sum is 43.

The spelling of 21818363821 in words is "twenty-one billion, eight hundred eighteen million, three hundred sixty-three thousand, eight hundred twenty-one".