642878261 has 2 divisors, whose sum is σ = 642878262. Its totient is φ = 642878260.

The previous prime is 642878209. The next prime is 642878297. The reversal of 642878261 is 162878246.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 630311236 + 12567025 = 25106^2 + 3545^2 .

It is a cyclic number.

It is not a de Polignac number, because 642878261 - 2¹⁰ = 642877237 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (642878861) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321439130 + 321439131.

It is an arithmetic number, because the mean of its divisors is an integer number (321439131).

Almost surely, 2^642878261 is an apocalyptic number.

It is an amenable number.

642878261 is a deficient number, since it is larger than the sum of its proper divisors (1).

642878261 is an equidigital number, since it uses as much as digits as its factorization.

642878261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 258048, while the sum is 44.

The square root of 642878261 is about 25355.0440938287. The cubic root of 642878261 is about 863.0638244670.

The spelling of 642878261 in words is "six hundred forty-two million, eight hundred seventy-eight thousand, two hundred sixty-one".