643825961 has 2 divisors, whose sum is σ = 643825962. Its totient is φ = 643825960.

The previous prime is 643825939. The next prime is 643825967. The reversal of 643825961 is 169528346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 332515225 + 311310736 = 18235^2 + 17644^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643825961 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (643825967) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321912980 + 321912981.

It is an arithmetic number, because the mean of its divisors is an integer number (321912981).

Almost surely, 2^643825961 is an apocalyptic number.

It is an amenable number.

643825961 is a deficient number, since it is larger than the sum of its proper divisors (1).

643825961 is an equidigital number, since it uses as much as digits as its factorization.

643825961 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 311040, while the sum is 44.

The square root of 643825961 is about 25373.7258005205. The cubic root of 643825961 is about 863.4877118753.

The spelling of 643825961 in words is "six hundred forty-three million, eight hundred twenty-five thousand, nine hundred sixty-one".