640649 has 2 divisors, whose sum is σ = 640650. Its totient is φ = 640648.

The previous prime is 640631. The next prime is 640663. The reversal of 640649 is 946046.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 573049 + 67600 = 757^2 + 260^2 .

It is a cyclic number.

It is not a de Polignac number, because 640649 - 2¹² = 636553 is a prime.

It is a super-2 number, since 2×640649² = 820862282402, which contains 22 as substring.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640649.

It is not a weakly prime, because it can be changed into another prime (640669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320324 + 320325.

It is an arithmetic number, because the mean of its divisors is an integer number (320325).

2⁶⁴⁰⁶⁴⁹ is an apocalyptic number.

It is an amenable number.

640649 is a deficient number, since it is larger than the sum of its proper divisors (1).

640649 is an equidigital number, since it uses as much as digits as its factorization.

640649 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 640649 is about 800.4055222198. The cubic root of 640649 is about 86.2065075127.

The spelling of 640649 in words is "six hundred forty thousand, six hundred forty-nine".