81617021 has 4 divisors (see below), whose sum is σ = 81920700. Its totient is φ = 81313344.

The previous prime is 81617009. The next prime is 81617023. The reversal of 81617021 is 12071618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8702500 + 72914521 = 2950^2 + 8539^2 .

It is a cyclic number.

It is not a de Polignac number, because 81617021 - 2¹⁴ = 81600637 is a prime.

It is a super-2 number, since 2×81617021² = 13322676233828882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81617023) 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, 151436 + ... + 151973.

It is an arithmetic number, because the mean of its divisors is an integer number (20480175).

Almost surely, 2^81617021 is an apocalyptic number.

It is an amenable number.

81617021 is a deficient number, since it is larger than the sum of its proper divisors (303679).

81617021 is a wasteful number, since it uses less digits than its factorization.

81617021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 303678.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 81617021 is about 9034.2139115697. The cubic root of 81617021 is about 433.7707330349.

Adding to 81617021 its reverse (12071618), we get a palindrome (93688639).

The spelling of 81617021 in words is "eighty-one million, six hundred seventeen thousand, twenty-one".