646743961 has 2 divisors, whose sum is σ = 646743962. Its totient is φ = 646743960.

The previous prime is 646743959. The next prime is 646743967. The reversal of 646743961 is 169347646.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 625950361 + 20793600 = 25019^2 + 4560^2 .

It is a cyclic number.

It is not a de Polignac number, because 646743961 - 2¹ = 646743959 is a prime.

Together with 646743959, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (646743967) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 323371980 + 323371981.

It is an arithmetic number, because the mean of its divisors is an integer number (323371981).

Almost surely, 2^646743961 is an apocalyptic number.

It is an amenable number.

646743961 is a deficient number, since it is larger than the sum of its proper divisors (1).

646743961 is an equidigital number, since it uses as much as digits as its factorization.

646743961 is an evil number, because the sum of its binary digits is even.

The product of its digits is 653184, while the sum is 46.

The square root of 646743961 is about 25431.1612200466. The cubic root of 646743961 is about 864.7902689087.

It can be divided in two parts, 64674 and 3961, that added together give a triangular number (68635 = T₃₇₀).

The spelling of 646743961 in words is "six hundred forty-six million, seven hundred forty-three thousand, nine hundred sixty-one".