644154661 has 2 divisors, whose sum is σ = 644154662. Its totient is φ = 644154660.

The previous prime is 644154653. The next prime is 644154689. The reversal of 644154661 is 166451446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 537961636 + 106193025 = 23194^2 + 10305^2 .

It is a cyclic number.

It is not a de Polignac number, because 644154661 - 2³ = 644154653 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644154661.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644154631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322077330 + 322077331.

It is an arithmetic number, because the mean of its divisors is an integer number (322077331).

Almost surely, 2^644154661 is an apocalyptic number.

It is an amenable number.

644154661 is a deficient number, since it is larger than the sum of its proper divisors (1).

644154661 is an equidigital number, since it uses as much as digits as its factorization.

644154661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 69120, while the sum is 37.

The square root of 644154661 is about 25380.2021465551. The cubic root of 644154661 is about 863.6346357024.

The spelling of 644154661 in words is "six hundred forty-four million, one hundred fifty-four thousand, six hundred sixty-one".