81699840 has 220 divisors, whose sum is σ = 294252156. Its totient is φ = 21676032.

The previous prime is 81699823. The next prime is 81699847. The reversal of 81699840 is 4899618.

It can be written as a sum of positive squares in 2 ways, for example, as 60466176 + 21233664 = 7776^2 + 4608^2 .

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81699847) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 414622 + ... + 414818.

Almost surely, 2^81699840 is an apocalyptic number.

81699840 is a gapful number since it is divisible by the number (80) 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 81699840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (147126078).

81699840 is an abundant number, since it is smaller than the sum of its proper divisors (212552316).

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

81699840 is a wasteful number, since it uses less digits than its factorization.

81699840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 234 (or 207 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 45.

The square root of 81699840 is about 9038.7963800497. The cubic root of 81699840 is about 433.9174030701.

The spelling of 81699840 in words is "eighty-one million, six hundred ninety-nine thousand, eight hundred forty".