81638401 has 16 divisors (see below), whose sum is σ = 89844048. Its totient is φ = 73728000.

The previous prime is 81638399. The next prime is 81638411. The reversal of 81638401 is 10483618.

It can be written as a sum of positive squares in 8 ways, for example, as 7420176 + 74218225 = 2724^2 + 8615^2 .

It is a 2-Lehmer number, since φ(81638401) divides (81638401-1)².

It is a cyclic number.

It is a Carmichael number.

It is not a de Polignac number, because 81638401 - 2¹ = 81638399 is a prime.

It is a deceptive number, since it divides R_81638400.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81638411) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 127041 + ... + 127681.

It is an arithmetic number, because the mean of its divisors is an integer number (5615253).

It is a Poulet number, since it divides 2^81638400-1.

Almost surely, 2^81638401 is an apocalyptic number.

It is an amenable number.

81638401 is a deficient number, since it is larger than the sum of its proper divisors (8205647).

81638401 is a wasteful number, since it uses less digits than its factorization.

81638401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 852.

The product of its (nonzero) digits is 4608, while the sum is 31.

The square root of 81638401 is about 9035.3971135750. The cubic root of 81638401 is about 433.8086058891.

It can be divided in two parts, 81 and 638401, that multiplied together give a square (51710481 = 7191²).

The spelling of 81638401 in words is "eighty-one million, six hundred thirty-eight thousand, four hundred one".