81303521 has 4 divisors (see below), whose sum is σ = 87557652. Its totient is φ = 75049392.

The previous prime is 81303517. The next prime is 81303529. The reversal of 81303521 is 12530318.

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 20151121 + 61152400 = 4489^2 + 7820^2 .

It is a cyclic number.

It is not a de Polignac number, because 81303521 - 2² = 81303517 is a prime.

It is a super-2 number, since 2×81303521² = 13220525053994882, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81303529) 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, 3127046 + ... + 3127071.

It is an arithmetic number, because the mean of its divisors is an integer number (21889413).

Almost surely, 2^81303521 is an apocalyptic number.

It is an amenable number.

81303521 is a deficient number, since it is larger than the sum of its proper divisors (6254131).

81303521 is a wasteful number, since it uses less digits than its factorization.

81303521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6254130.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 81303521 is about 9016.8465108374. The cubic root of 81303521 is about 433.2146333002.

Adding to 81303521 its reverse (12530318), we get a palindrome (93833839).

The spelling of 81303521 in words is "eighty-one million, three hundred three thousand, five hundred twenty-one".