81221616 has 150 divisors (see below), whose sum is σ = 273672960. Its totient is φ = 23188032.

The previous prime is 81221603. The next prime is 81221617. The reversal of 81221616 is 61612218.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 81221616.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81221617) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 62865 + ... + 64143.

Almost surely, 2^81221616 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81221616, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (136836480).

81221616 is an abundant number, since it is smaller than the sum of its proper divisors (192451344).

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

81221616 is a wasteful number, since it uses less digits than its factorization.

81221616 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1313 (or 1291 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 81221616 is about 9012.3035900928. The cubic root of 81221616 is about 433.0691112459.

The spelling of 81221616 in words is "eighty-one million, two hundred twenty-one thousand, six hundred sixteen".