81638533 has 2 divisors, whose sum is σ = 81638534. Its totient is φ = 81638532.

The previous prime is 81638519. The next prime is 81638549. The reversal of 81638533 is 33583618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 56055169 + 25583364 = 7487^2 + 5058^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81638533 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81638492 and 81638501.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81638563) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40819266 + 40819267.

It is an arithmetic number, because the mean of its divisors is an integer number (40819267).

Almost surely, 2^81638533 is an apocalyptic number.

It is an amenable number.

81638533 is a deficient number, since it is larger than the sum of its proper divisors (1).

81638533 is an equidigital number, since it uses as much as digits as its factorization.

81638533 is an evil number, because the sum of its binary digits is even.

The product of its digits is 51840, while the sum is 37.

The square root of 81638533 is about 9035.4044181763. The cubic root of 81638533 is about 433.8088396953.

The spelling of 81638533 in words is "eighty-one million, six hundred thirty-eight thousand, five hundred thirty-three".