81812921 has 2 divisors, whose sum is σ = 81812922. Its totient is φ = 81812920.

The previous prime is 81812897. The next prime is 81812933. The reversal of 81812921 is 12921818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 74995600 + 6817321 = 8660^2 + 2611^2 .

It is a cyclic number.

It is not a de Polignac number, because 81812921 - 2²⁶ = 14704057 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (81812971) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40906460 + 40906461.

It is an arithmetic number, because the mean of its divisors is an integer number (40906461).

Almost surely, 2^81812921 is an apocalyptic number.

It is an amenable number.

81812921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81812921 is an equidigital number, since it uses as much as digits as its factorization.

81812921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2304, while the sum is 32.

The square root of 81812921 is about 9045.0495299915. The cubic root of 81812921 is about 434.1175062483.

The spelling of 81812921 in words is "eighty-one million, eight hundred twelve thousand, nine hundred twenty-one".