918191021221 has 2 divisors, whose sum is σ = 918191021222. Its totient is φ = 918191021220.

The previous prime is 918191021191. The next prime is 918191021263. The reversal of 918191021221 is 122120191819.

918191021221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 560364530625 + 357826490596 = 748575^2 + 598186^2 .

It is an emirp because it is prime and its reverse (122120191819) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 918191021221 - 2²³ = 918182632613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (918191021021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 459095510610 + 459095510611.

It is an arithmetic number, because the mean of its divisors is an integer number (459095510611).

Almost surely, 2^918191021221 is an apocalyptic number.

It is an amenable number.

918191021221 is a deficient number, since it is larger than the sum of its proper divisors (1).

918191021221 is an equidigital number, since it uses as much as digits as its factorization.

918191021221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 37.

The spelling of 918191021221 in words is "nine hundred eighteen billion, one hundred ninety-one million, twenty-one thousand, two hundred twenty-one".