81220817 has 4 divisors (see below), whose sum is σ = 82433136. Its totient is φ = 80008500.

The previous prime is 81220807. The next prime is 81220823. The reversal of 81220817 is 71802218.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81220817 - 2¹⁰ = 81219793 is a prime.

It is a super-2 number, since 2×81220817² = 13193642228294978, which contains 22 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 81220817.

It is not an unprimeable number, because it can be changed into a prime (81220807) 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, 606059 + ... + 606192.

It is an arithmetic number, because the mean of its divisors is an integer number (20608284).

Almost surely, 2^81220817 is an apocalyptic number.

It is an amenable number.

81220817 is a deficient number, since it is larger than the sum of its proper divisors (1212319).

81220817 is a wasteful number, since it uses less digits than its factorization.

81220817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1212318.

The product of its (nonzero) digits is 1792, while the sum is 29.

The square root of 81220817 is about 9012.2592616946. The cubic root of 81220817 is about 433.0676911669.

The spelling of 81220817 in words is "eighty-one million, two hundred twenty thousand, eight hundred seventeen".