81220639 has 4 divisors (see below), whose sum is σ = 82597320. Its totient is φ = 79843960.

The previous prime is 81220637. The next prime is 81220669. The reversal of 81220639 is 93602218.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 93602218 = 2 ⋅46801109.

It is a cyclic number.

It is not a de Polignac number, because 81220639 - 2¹ = 81220637 is a prime.

It is a super-3 number, since 3×81220639³ (a number of 25 digits) contains 333 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81220639.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81220637) 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, 688252 + ... + 688369.

It is an arithmetic number, because the mean of its divisors is an integer number (20649330).

Almost surely, 2^81220639 is an apocalyptic number.

81220639 is a deficient number, since it is larger than the sum of its proper divisors (1376681).

81220639 is a wasteful number, since it uses less digits than its factorization.

81220639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1376680.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 81220639 is about 9012.2493862520. The cubic root of 81220639 is about 433.0673748025.

The spelling of 81220639 in words is "eighty-one million, two hundred twenty thousand, six hundred thirty-nine".