81425821 has 2 divisors, whose sum is σ = 81425822. Its totient is φ = 81425820.

The previous prime is 81425807. The next prime is 81425831. The reversal of 81425821 is 12852418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 53494596 + 27931225 = 7314^2 + 5285^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81425821 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81425831) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40712910 + 40712911.

It is an arithmetic number, because the mean of its divisors is an integer number (40712911).

Almost surely, 2^81425821 is an apocalyptic number.

It is an amenable number.

81425821 is a deficient number, since it is larger than the sum of its proper divisors (1).

81425821 is an equidigital number, since it uses as much as digits as its factorization.

81425821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5120, while the sum is 31.

The square root of 81425821 is about 9023.6257125393. The cubic root of 81425821 is about 433.4317440528.

The spelling of 81425821 in words is "eighty-one million, four hundred twenty-five thousand, eight hundred twenty-one".