81605972 has 36 divisors (see below), whose sum is σ = 166742100. Its totient is φ = 34844544.

The previous prime is 81605957. The next prime is 81605989. The reversal of 81605972 is 27950618.

It can be written as a sum of positive squares in 2 ways, for example, as 51179716 + 30426256 = 7154^2 + 5516^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 67808 + ... + 69000.

It is an arithmetic number, because the mean of its divisors is an integer number (4631725).

Almost surely, 2^81605972 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81605972, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (83371050).

81605972 is an abundant number, since it is smaller than the sum of its proper divisors (85136128).

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

81605972 is a wasteful number, since it uses less digits than its factorization.

81605972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1560 (or 1551 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 81605972 is about 9033.6023822172. The cubic root of 81605972 is about 433.7511580776.

The spelling of 81605972 in words is "eighty-one million, six hundred five thousand, nine hundred seventy-two".