9121778021 has 2 divisors, whose sum is σ = 9121778022. Its totient is φ = 9121778020.

The previous prime is 9121777981. The next prime is 9121778023. The reversal of 9121778021 is 1208771219.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 8849164900 + 272613121 = 94070^2 + 16511^2 .

It is an emirp because it is prime and its reverse (1208771219) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 9121778021 - 2¹⁰ = 9121776997 is a prime.

Together with 9121778023, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (9121778023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4560889010 + 4560889011.

It is an arithmetic number, because the mean of its divisors is an integer number (4560889011).

Almost surely, 2^9121778021 is an apocalyptic number.

It is an amenable number.

9121778021 is a deficient number, since it is larger than the sum of its proper divisors (1).

9121778021 is an equidigital number, since it uses as much as digits as its factorization.

9121778021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 14112, while the sum is 38.

The square root of 9121778021 is about 95507.9997748880. Note that the first 3 decimals coincide. The cubic root of 9121778021 is about 2089.4236195911.

The spelling of 9121778021 in words is "nine billion, one hundred twenty-one million, seven hundred seventy-eight thousand, twenty-one".