642626209 has 2 divisors, whose sum is σ = 642626210. Its totient is φ = 642626208.

The previous prime is 642626203. The next prime is 642626213. The reversal of 642626209 is 902626246.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 459159184 + 183467025 = 21428^2 + 13545^2 .

It is a cyclic number.

It is not a de Polignac number, because 642626209 - 2¹¹ = 642624161 is a prime.

It is not a weakly prime, because it can be changed into another prime (642626203) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321313104 + 321313105.

It is an arithmetic number, because the mean of its divisors is an integer number (321313105).

Almost surely, 2^642626209 is an apocalyptic number.

It is an amenable number.

642626209 is a deficient number, since it is larger than the sum of its proper divisors (1).

642626209 is an equidigital number, since it uses as much as digits as its factorization.

642626209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 62208, while the sum is 37.

The square root of 642626209 is about 25350.0731557130. The cubic root of 642626209 is about 862.9510164844.

Adding to 642626209 its sum of digits (37), we get a palindrome (642626246).

The spelling of 642626209 in words is "six hundred forty-two million, six hundred twenty-six thousand, two hundred nine".