81202021 has 4 divisors (see below), whose sum is σ = 81614412. Its totient is φ = 80789632.

The previous prime is 81201997. The next prime is 81202027. The reversal of 81202021 is 12020218.

81202021 = 243² + 244² + ... + 636².

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 76300225 + 4901796 = 8735^2 + 2214^2 .

It is a cyclic number.

It is not a de Polignac number, because 81202021 - 2⁹ = 81201509 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81201986 and 81202004.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81202027) 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, 205900 + ... + 206293.

It is an arithmetic number, because the mean of its divisors is an integer number (20403603).

Almost surely, 2^81202021 is an apocalyptic number.

It is an amenable number.

81202021 is a deficient number, since it is larger than the sum of its proper divisors (412391).

81202021 is a wasteful number, since it uses less digits than its factorization.

81202021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 412390.

The product of its (nonzero) digits is 64, while the sum is 16.

The square root of 81202021 is about 9011.2163995767. The cubic root of 81202021 is about 433.0342819638.

Adding to 81202021 its reverse (12020218), we get a palindrome (93222239).

The spelling of 81202021 in words is "eighty-one million, two hundred two thousand, twenty-one".