81621520 has 20 divisors (see below), whose sum is σ = 189770220. Its totient is φ = 32648576.

The previous prime is 81621517. The next prime is 81621521. The reversal of 81621520 is 2512618.

It can be written as a sum of positive squares in 2 ways, for example, as 64448784 + 17172736 = 8028^2 + 4144^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a super-2 number, since 2×81621520² = 13324145054220800, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81621521) 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, 510055 + ... + 510214.

It is an arithmetic number, because the mean of its divisors is an integer number (9488511).

Almost surely, 2^81621520 is an apocalyptic number.

81621520 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81621520 is an abundant number, since it is smaller than the sum of its proper divisors (108148700).

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

81621520 is a wasteful number, since it uses less digits than its factorization.

81621520 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1020282 (or 1020276 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 81621520 is about 9034.4629060061. The cubic root of 81621520 is about 433.7787031807.

The spelling of 81621520 in words is "eighty-one million, six hundred twenty-one thousand, five hundred twenty".