81750821 has 2 divisors, whose sum is σ = 81750822. Its totient is φ = 81750820.

The previous prime is 81750817. The next prime is 81750827. The reversal of 81750821 is 12805718.

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., 47761921 + 33988900 = 6911^2 + 5830^2 .

It is a cyclic number.

It is not a de Polignac number, because 81750821 - 2² = 81750817 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81750827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40875410 + 40875411.

It is an arithmetic number, because the mean of its divisors is an integer number (40875411).

Almost surely, 2^81750821 is an apocalyptic number.

It is an amenable number.

81750821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81750821 is an equidigital number, since it uses as much as digits as its factorization.

81750821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4480, while the sum is 32.

The square root of 81750821 is about 9041.6160613023. The cubic root of 81750821 is about 434.0076396540.

The spelling of 81750821 in words is "eighty-one million, seven hundred fifty thousand, eight hundred twenty-one".