91781640 has 128 divisors (see below), whose sum is σ = 324000000. Its totient is φ = 23030784.

The previous prime is 91781617. The next prime is 91781663. The reversal of 91781640 is 4618719.

91781640 is a `hidden beast` number, since 9 + 1 + 7 + 8 + 1 + 640 = 666.

It is an interprime number because it is at equal distance from previous prime (91781617) and next prime (91781663).

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

It is a junction number, because it is equal to n+sod(n) for n = 91781595 and 91781604.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 15861 + ... + 20859.

It is an arithmetic number, because the mean of its divisors is an integer number (2531250).

Almost surely, 2^91781640 is an apocalyptic number.

91781640 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 91781640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (162000000).

91781640 is an abundant number, since it is smaller than the sum of its proper divisors (232218360).

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

91781640 is a wasteful number, since it uses less digits than its factorization.

91781640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5036 (or 5026 counting only the distinct ones).

The product of its (nonzero) digits is 12096, while the sum is 36.

The square root of 91781640 is about 9580.2734825265. The cubic root of 91781640 is about 451.0783029644.

The spelling of 91781640 in words is "ninety-one million, seven hundred eighty-one thousand, six hundred forty".