21205890490597 has 2 divisors, whose sum is σ = 21205890490598. Its totient is φ = 21205890490596.

The previous prime is 21205890490549. The next prime is 21205890490607. The reversal of 21205890490597 is 79509409850212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19237969704321 + 1967920786276 = 4386111^2 + 1402826^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21205890490597 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21205890490297) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602945245298 + 10602945245299.

It is an arithmetic number, because the mean of its divisors is an integer number (10602945245299).

Almost surely, 2^{21205890490597} is an apocalyptic number.

It is an amenable number.

21205890490597 is a deficient number, since it is larger than the sum of its proper divisors (1).

21205890490597 is an equidigital number, since it uses as much as digits as its factorization.

21205890490597 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16329600, while the sum is 61.

The spelling of 21205890490597 in words is "twenty-one trillion, two hundred five billion, eight hundred ninety million, four hundred ninety thousand, five hundred ninety-seven".