991209208537 has 2 divisors, whose sum is σ = 991209208538. Its totient is φ = 991209208536.

The previous prime is 991209208531. The next prime is 991209208559. The reversal of 991209208537 is 735802902199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 936667809856 + 54541398681 = 967816^2 + 233541^2 .

It is a cyclic number.

It is not a de Polignac number, because 991209208537 - 2²⁷ = 991074990809 is a prime.

It is not a weakly prime, because it can be changed into another prime (991209208531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495604604268 + 495604604269.

It is an arithmetic number, because the mean of its divisors is an integer number (495604604269).

Almost surely, 2^991209208537 is an apocalyptic number.

It is an amenable number.

991209208537 is a deficient number, since it is larger than the sum of its proper divisors (1).

991209208537 is an equidigital number, since it uses as much as digits as its factorization.

991209208537 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2449440, while the sum is 55.

The spelling of 991209208537 in words is "nine hundred ninety-one billion, two hundred nine million, two hundred eight thousand, five hundred thirty-seven".