642381991 has 2 divisors, whose sum is σ = 642381992. Its totient is φ = 642381990.

The previous prime is 642381937. The next prime is 642382021. The reversal of 642381991 is 199183246.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 642381991 - 2²¹ = 640284839 is a prime.

It is a super-2 number, since 2×642381991² = 825309244722248162, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (642381791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321190995 + 321190996.

It is an arithmetic number, because the mean of its divisors is an integer number (321190996).

Almost surely, 2^642381991 is an apocalyptic number.

642381991 is a deficient number, since it is larger than the sum of its proper divisors (1).

642381991 is an equidigital number, since it uses as much as digits as its factorization.

642381991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 93312, while the sum is 43.

The square root of 642381991 is about 25345.2557888059. The cubic root of 642381991 is about 862.8416865343.

The spelling of 642381991 in words is "six hundred forty-two million, three hundred eighty-one thousand, nine hundred ninety-one".