642881221 has 2 divisors, whose sum is σ = 642881222. Its totient is φ = 642881220.

The previous prime is 642881219. The next prime is 642881243. The reversal of 642881221 is 122188246.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 625700196 + 17181025 = 25014^2 + 4145^2 .

It is a cyclic number.

It is not a de Polignac number, because 642881221 - 2¹ = 642881219 is a prime.

Together with 642881219, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (642881201) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321440610 + 321440611.

It is an arithmetic number, because the mean of its divisors is an integer number (321440611).

Almost surely, 2^642881221 is an apocalyptic number.

It is an amenable number.

642881221 is a deficient number, since it is larger than the sum of its proper divisors (1).

642881221 is an equidigital number, since it uses as much as digits as its factorization.

642881221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12288, while the sum is 34.

The square root of 642881221 is about 25355.1024647900. The cubic root of 642881221 is about 863.0651490646.

The spelling of 642881221 in words is "six hundred forty-two million, eight hundred eighty-one thousand, two hundred twenty-one".