491209021 has 2 divisors, whose sum is σ = 491209022. Its totient is φ = 491209020.

The previous prime is 491209009. The next prime is 491209049. The reversal of 491209021 is 120902194.

It is a happy number.

It is an a-pointer prime, because the next prime (491209049) can be obtained adding 491209021 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 304886521 + 186322500 = 17461^2 + 13650^2 .

It is a cyclic number.

It is not a de Polignac number, because 491209021 - 2¹¹ = 491206973 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (491209001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 245604510 + 245604511.

It is an arithmetic number, because the mean of its divisors is an integer number (245604511).

Almost surely, 2^491209021 is an apocalyptic number.

It is an amenable number.

491209021 is a deficient number, since it is larger than the sum of its proper divisors (1).

491209021 is an equidigital number, since it uses as much as digits as its factorization.

491209021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 491209021 is about 22163.2357971484. The cubic root of 491209021 is about 789.0213920049.

The spelling of 491209021 in words is "four hundred ninety-one million, two hundred nine thousand, twenty-one".