81638399 has 2 divisors, whose sum is σ = 81638400. Its totient is φ = 81638398.

The previous prime is 81638377. The next prime is 81638411. The reversal of 81638399 is 99383618.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81638399 - 2²⁴ = 64861183 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81638329) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40819199 + 40819200.

It is an arithmetic number, because the mean of its divisors is an integer number (40819200).

Almost surely, 2^81638399 is an apocalyptic number.

81638399 is a deficient number, since it is larger than the sum of its proper divisors (1).

81638399 is an equidigital number, since it uses as much as digits as its factorization.

81638399 is an evil number, because the sum of its binary digits is even.

The product of its digits is 279936, while the sum is 47.

The square root of 81638399 is about 9035.3970028992. The cubic root of 81638399 is about 433.8086023466.

The spelling of 81638399 in words is "eighty-one million, six hundred thirty-eight thousand, three hundred ninety-nine".