991378621 has 4 divisors (see below), whose sum is σ = 1010083932. Its totient is φ = 972673312.

The previous prime is 991378607. The next prime is 991378627. The reversal of 991378621 is 126873199.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 126873199 = 503 ⋅252233.

It can be written as a sum of positive squares in 2 ways, for example, as 905167396 + 86211225 = 30086^2 + 9285^2 .

It is a cyclic number.

It is not a de Polignac number, because 991378621 - 2⁵ = 991378589 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991378627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9352576 + ... + 9352681.

It is an arithmetic number, because the mean of its divisors is an integer number (252520983).

Almost surely, 2^991378621 is an apocalyptic number.

It is an amenable number.

991378621 is a deficient number, since it is larger than the sum of its proper divisors (18705311).

991378621 is a wasteful number, since it uses less digits than its factorization.

991378621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18705310.

The product of its digits is 163296, while the sum is 46.

The square root of 991378621 is about 31486.1655493329. The cubic root of 991378621 is about 997.1179085287.

The spelling of 991378621 in words is "nine hundred ninety-one million, three hundred seventy-eight thousand, six hundred twenty-one".