81399421 has 2 divisors, whose sum is σ = 81399422. Its totient is φ = 81399420.

The previous prime is 81399413. The next prime is 81399431. The reversal of 81399421 is 12499318.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 80371225 + 1028196 = 8965^2 + 1014^2 .

It is a cyclic number.

It is not a de Polignac number, because 81399421 - 2³ = 81399413 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81399431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40699710 + 40699711.

It is an arithmetic number, because the mean of its divisors is an integer number (40699711).

Almost surely, 2^81399421 is an apocalyptic number.

It is an amenable number.

81399421 is a deficient number, since it is larger than the sum of its proper divisors (1).

81399421 is an equidigital number, since it uses as much as digits as its factorization.

81399421 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 15552, while the sum is 37.

The square root of 81399421 is about 9022.1627673192. The cubic root of 81399421 is about 433.3848963625.

The spelling of 81399421 in words is "eighty-one million, three hundred ninety-nine thousand, four hundred twenty-one".