991621620 has 144 divisors (see below), whose sum is σ = 3309284160. Its totient is φ = 240335040.

The previous prime is 991621607. The next prime is 991621633. The reversal of 991621620 is 26126199.

991621620 is a `hidden beast` number, since 9 + 9 + 1 + 6 + 21 + 620 = 666.

It is an interprime number because it is at equal distance from previous prime (991621607) and next prime (991621633).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 237511 + ... + 241649.

It is an arithmetic number, because the mean of its divisors is an integer number (22981140).

Almost surely, 2^991621620 is an apocalyptic number.

991621620 is a gapful number since it is divisible by the number (90) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 991621620, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1654642080).

991621620 is an abundant number, since it is smaller than the sum of its proper divisors (2317662540).

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

991621620 is a wasteful number, since it uses less digits than its factorization.

991621620 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4187 (or 4160 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 36.

The square root of 991621620 is about 31490.0241346367. The cubic root of 991621620 is about 997.1993704631.

The spelling of 991621620 in words is "nine hundred ninety-one million, six hundred twenty-one thousand, six hundred twenty".