642220021 has 2 divisors, whose sum is σ = 642220022. Its totient is φ = 642220020.

The previous prime is 642220009. The next prime is 642220031. The reversal of 642220021 is 120022246.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 625500100 + 16719921 = 25010^2 + 4089^2 .

It is a cyclic number.

It is not a de Polignac number, because 642220021 - 2¹⁵ = 642187253 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (642220031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321110010 + 321110011.

It is an arithmetic number, because the mean of its divisors is an integer number (321110011).

Almost surely, 2^642220021 is an apocalyptic number.

It is an amenable number.

642220021 is a deficient number, since it is larger than the sum of its proper divisors (1).

642220021 is an equidigital number, since it uses as much as digits as its factorization.

642220021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 384, while the sum is 19.

The square root of 642220021 is about 25342.0603148205. The cubic root of 642220021 is about 862.7691615583.

Adding to 642220021 its reverse (120022246), we get a palindrome (762242267).

The spelling of 642220021 in words is "six hundred forty-two million, two hundred twenty thousand, twenty-one".