81377521 has 4 divisors (see below), whose sum is σ = 86164452. Its totient is φ = 76590592.

The previous prime is 81377507. The next prime is 81377537. The reversal of 81377521 is 12577318.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 34386496 + 46991025 = 5864^2 + 6855^2 .

It is a cyclic number.

It is not a de Polignac number, because 81377521 - 2¹¹ = 81375473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81377501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2393440 + ... + 2393473.

It is an arithmetic number, because the mean of its divisors is an integer number (21541113).

Almost surely, 2^81377521 is an apocalyptic number.

It is an amenable number.

81377521 is a deficient number, since it is larger than the sum of its proper divisors (4786931).

81377521 is a wasteful number, since it uses less digits than its factorization.

81377521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4786930.

The product of its digits is 11760, while the sum is 34.

The square root of 81377521 is about 9020.9490077264. The cubic root of 81377521 is about 433.3460263869.

The spelling of 81377521 in words is "eighty-one million, three hundred seventy-seven thousand, five hundred twenty-one".