991721400 has 48 divisors (see below), whose sum is σ = 3074338200. Its totient is φ = 264458880.

The previous prime is 991721387. The next prime is 991721413. The reversal of 991721400 is 4127199.

It is an interprime number because it is at equal distance from previous prime (991721387) and next prime (991721413).

It is a super-2 number, since 2×991721400² = 1967022670435920000, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 825835 + ... + 827034.

Almost surely, 2^991721400 is an apocalyptic number.

It is an amenable number.

991721400 is an abundant number, since it is smaller than the sum of its proper divisors (2082616800).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

991721400 is a wasteful number, since it uses less digits than its factorization.

991721400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1652888 (or 1652879 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 33.

The square root of 991721400 is about 31491.6084060500. The cubic root of 991721400 is about 997.2328164248.

Adding to 991721400 its reverse (4127199), we get a palindrome (995848599).

The spelling of 991721400 in words is "nine hundred ninety-one million, seven hundred twenty-one thousand, four hundred".