81371021 has 2 divisors, whose sum is σ = 81371022. Its totient is φ = 81371020.

The previous prime is 81370997. The next prime is 81371051. The reversal of 81371021 is 12017318.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 60668521 + 20702500 = 7789^2 + 4550^2 .

It is a cyclic number.

It is not a de Polignac number, because 81371021 - 2⁶ = 81370957 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81371051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40685510 + 40685511.

It is an arithmetic number, because the mean of its divisors is an integer number (40685511).

Almost surely, 2^81371021 is an apocalyptic number.

It is an amenable number.

81371021 is a deficient number, since it is larger than the sum of its proper divisors (1).

81371021 is an equidigital number, since it uses as much as digits as its factorization.

81371021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 336, while the sum is 23.

The square root of 81371021 is about 9020.5887280155. The cubic root of 81371021 is about 433.3344882941.

Adding to 81371021 its reverse (12017318), we get a palindrome (93388339).

The spelling of 81371021 in words is "eighty-one million, three hundred seventy-one thousand, twenty-one".