21203570821 has 2 divisors, whose sum is σ = 21203570822. Its totient is φ = 21203570820.

The previous prime is 21203570767. The next prime is 21203570831. The reversal of 21203570821 is 12807530212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20754724225 + 448846596 = 144065^2 + 21186^2 .

It is a cyclic number.

It is not a de Polignac number, because 21203570821 - 2¹³ = 21203562629 is a prime.

It is a super-2 number, since 2×21203570821² (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 (21203570831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10601785410 + 10601785411.

It is an arithmetic number, because the mean of its divisors is an integer number (10601785411).

Almost surely, 2^21203570821 is an apocalyptic number.

It is an amenable number.

21203570821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21203570821 is an equidigital number, since it uses as much as digits as its factorization.

21203570821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6720, while the sum is 31.

The spelling of 21203570821 in words is "twenty-one billion, two hundred three million, five hundred seventy thousand, eight hundred twenty-one".