643129961 has 2 divisors, whose sum is σ = 643129962. Its totient is φ = 643129960.

The previous prime is 643129951. The next prime is 643129969. The reversal of 643129961 is 169921346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 643129600 + 361 = 25360^2 + 19^2 .

It is a cyclic number.

It is not a de Polignac number, because 643129961 - 2¹⁸ = 642867817 is a prime.

It is a super-2 number, since 2×643129961² = 827232293471723042, which contains 22 as substring.

It is equal to p_33454895 and since 643129961 and 33454895 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (643129969) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321564980 + 321564981.

It is an arithmetic number, because the mean of its divisors is an integer number (321564981).

Almost surely, 2^643129961 is an apocalyptic number.

It is an amenable number.

643129961 is a deficient number, since it is larger than the sum of its proper divisors (1).

643129961 is an equidigital number, since it uses as much as digits as its factorization.

643129961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 69984, while the sum is 41.

The square root of 643129961 is about 25360.0071175069. The cubic root of 643129961 is about 863.1764454890.

The spelling of 643129961 in words is "six hundred forty-three million, one hundred twenty-nine thousand, nine hundred sixty-one".