81621820 has 24 divisors (see below), whose sum is σ = 195892704. Its totient is φ = 27984576.

The previous prime is 81621817. The next prime is 81621833. The reversal of 81621820 is 2812618.

It is a super-2 number, since 2×81621820² = 13324243000224800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 291367 + ... + 291646.

It is an arithmetic number, because the mean of its divisors is an integer number (8162196).

Almost surely, 2^81621820 is an apocalyptic number.

It is an amenable number.

81621820 is an abundant number, since it is smaller than the sum of its proper divisors (114270884).

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

81621820 is a wasteful number, since it uses less digits than its factorization.

81621820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 583029 (or 583027 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 28.

The square root of 81621820 is about 9034.4795090808. The cubic root of 81621820 is about 433.7792346315.

The spelling of 81621820 in words is "eighty-one million, six hundred twenty-one thousand, eight hundred twenty".