642021251 has 2 divisors, whose sum is σ = 642021252. Its totient is φ = 642021250.

The previous prime is 642021239. The next prime is 642021329. The reversal of 642021251 is 152120246.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 642021251 - 2¹⁰ = 642020227 is a prime.

It is not a weakly prime, because it can be changed into another prime (642021851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321010625 + 321010626.

It is an arithmetic number, because the mean of its divisors is an integer number (321010626).

Almost surely, 2^642021251 is an apocalyptic number.

642021251 is a deficient number, since it is larger than the sum of its proper divisors (1).

642021251 is an equidigital number, since it uses as much as digits as its factorization.

642021251 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 960, while the sum is 23.

The square root of 642021251 is about 25338.1382702045. The cubic root of 642021251 is about 862.6801420550.

Adding to 642021251 its reverse (152120246), we get a palindrome (794141497).

The spelling of 642021251 in words is "six hundred forty-two million, twenty-one thousand, two hundred fifty-one".