919997921 has 4 divisors (see below), whose sum is σ = 920080644. Its totient is φ = 919915200.

The previous prime is 919997867. The next prime is 919997963. The reversal of 919997921 is 129799919.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 129799919 = 6863 ⋅18913.

It can be written as a sum of positive squares in 2 ways, for example, as 737882896 + 182115025 = 27164^2 + 13495^2 .

It is a cyclic number.

It is not a de Polignac number, because 919997921 - 2¹⁸ = 919735777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (919997521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21500 + ... + 47981.

It is an arithmetic number, because the mean of its divisors is an integer number (230020161).

Almost surely, 2^919997921 is an apocalyptic number.

It is an amenable number.

919997921 is a deficient number, since it is larger than the sum of its proper divisors (82723).

919997921 is a wasteful number, since it uses less digits than its factorization.

919997921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 82722.

The product of its digits is 826686, while the sum is 56.

The square root of 919997921 is about 30331.4675048867. The cubic root of 919997921 is about 972.5880936052.

The spelling of 919997921 in words is "nine hundred nineteen million, nine hundred ninety-seven thousand, nine hundred twenty-one".