81372821 has 2 divisors, whose sum is σ = 81372822. Its totient is φ = 81372820.

The previous prime is 81372803. The next prime is 81372833. The reversal of 81372821 is 12827318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81180100 + 192721 = 9010^2 + 439^2 .

It is a cyclic number.

It is not a de Polignac number, because 81372821 - 2²⁶ = 14263957 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81372721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40686410 + 40686411.

It is an arithmetic number, because the mean of its divisors is an integer number (40686411).

Almost surely, 2^81372821 is an apocalyptic number.

It is an amenable number.

81372821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81372821 is an equidigital number, since it uses as much as digits as its factorization.

81372821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5376, while the sum is 32.

The square root of 81372821 is about 9020.6884992222. The cubic root of 81372821 is about 433.3376835198.

The spelling of 81372821 in words is "eighty-one million, three hundred seventy-two thousand, eight hundred twenty-one".