642937781 has 2 divisors, whose sum is σ = 642937782. Its totient is φ = 642937780.

The previous prime is 642937777. The next prime is 642937793. The reversal of 642937781 is 187739246.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 632271025 + 10666756 = 25145^2 + 3266^2 .

It is a cyclic number.

It is not a de Polignac number, because 642937781 - 2² = 642937777 is a prime.

It is a super-2 number, since 2×642937781² = 826737980474407922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (642937721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321468890 + 321468891.

It is an arithmetic number, because the mean of its divisors is an integer number (321468891).

Almost surely, 2^642937781 is an apocalyptic number.

It is an amenable number.

642937781 is a deficient number, since it is larger than the sum of its proper divisors (1).

642937781 is an equidigital number, since it uses as much as digits as its factorization.

642937781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 508032, while the sum is 47.

The square root of 642937781 is about 25356.2177976133. The cubic root of 642937781 is about 863.0904588376.

The spelling of 642937781 in words is "six hundred forty-two million, nine hundred thirty-seven thousand, seven hundred eighty-one".