81905670 has 192 divisors, whose sum is σ = 271724544. Its totient is φ = 16623360.

The previous prime is 81905653. The next prime is 81905683. The reversal of 81905670 is 7650918.

81905670 is a `hidden beast` number, since 8 + 1 + 90 + 567 + 0 = 666.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 367179 + ... + 367401.

It is an arithmetic number, because the mean of its divisors is an integer number (1415232).

Almost surely, 2^81905670 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81905670, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (135862272).

81905670 is an abundant number, since it is smaller than the sum of its proper divisors (189818874).

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

81905670 is a wasteful number, since it uses less digits than its factorization.

81905670 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 307 (or 304 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 36.

The square root of 81905670 is about 9050.1751364269. The cubic root of 81905670 is about 434.2814932172.

The spelling of 81905670 in words is "eighty-one million, nine hundred five thousand, six hundred seventy".