820642591 has 2 divisors, whose sum is σ = 820642592. Its totient is φ = 820642590.

The previous prime is 820642561. The next prime is 820642727. The reversal of 820642591 is 195246028.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 820642591 - 2⁷ = 820642463 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 820642591.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (820642531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410321295 + 410321296.

It is an arithmetic number, because the mean of its divisors is an integer number (410321296).

Almost surely, 2^820642591 is an apocalyptic number.

820642591 is a deficient number, since it is larger than the sum of its proper divisors (1).

820642591 is an equidigital number, since it uses as much as digits as its factorization.

820642591 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 34560, while the sum is 37.

The square root of 820642591 is about 28646.8600548123. The cubic root of 820642591 is about 936.2345939451.

The spelling of 820642591 in words is "eight hundred twenty million, six hundred forty-two thousand, five hundred ninety-one".