91021639680 has 336 divisors, whose sum is σ = 324135658560. Its totient is φ = 24234688512.

The previous prime is 91021639651. The next prime is 91021639697. The reversal of 91021639680 is 8693612019.

It is a happy number.

91021639680 is a `hidden beast` number, since 9 + 1 + 0 + 2 + 1 + 639 + 6 + 8 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 141557439 + ... + 141558081.

It is an arithmetic number, because the mean of its divisors is an integer number (964689460).

Almost surely, 2^91021639680 is an apocalyptic number.

91021639680 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 91021639680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (162067829280).

91021639680 is an abundant number, since it is smaller than the sum of its proper divisors (233114018880).

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

91021639680 is an frugal number, since it uses more digits than its factorization.

91021639680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 697 (or 653 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 45.

The spelling of 91021639680 in words is "ninety-one billion, twenty-one million, six hundred thirty-nine thousand, six hundred eighty".