81621780 has 48 divisors (see below), whose sum is σ = 232424640. Its totient is φ = 21395968.

The previous prime is 81621767. The next prime is 81621781. The reversal of 81621780 is 8712618.

It is a happy number.

It is a super-2 number, since 2×81621780² = 13324229940736800, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81621781) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7989 + ... + 15068.

It is an arithmetic number, because the mean of its divisors is an integer number (4842180).

Almost surely, 2^81621780 is an apocalyptic number.

It is an amenable number.

81621780 is an abundant number, since it is smaller than the sum of its proper divisors (150802860).

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

81621780 is a wasteful number, since it uses less digits than its factorization.

81621780 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23128 (or 23126 counting only the distinct ones).

The product of its (nonzero) digits is 5376, while the sum is 33.

The square root of 81621780 is about 9034.4772953392. The cubic root of 81621780 is about 433.7791637714.

The spelling of 81621780 in words is "eighty-one million, six hundred twenty-one thousand, seven hundred eighty".