81669557 has 2 divisors, whose sum is σ = 81669558. Its totient is φ = 81669556.

The previous prime is 81669551. The next prime is 81669607. The reversal of 81669557 is 75596618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50822641 + 30846916 = 7129^2 + 5554^2 .

It is a cyclic number.

It is not a de Polignac number, because 81669557 - 2⁴ = 81669541 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81669551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40834778 + 40834779.

It is an arithmetic number, because the mean of its divisors is an integer number (40834779).

Almost surely, 2^81669557 is an apocalyptic number.

It is an amenable number.

81669557 is a deficient number, since it is larger than the sum of its proper divisors (1).

81669557 is an equidigital number, since it uses as much as digits as its factorization.

81669557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 453600, while the sum is 47.

The square root of 81669557 is about 9037.1210570624. The cubic root of 81669557 is about 433.8637842601.

The spelling of 81669557 in words is "eighty-one million, six hundred sixty-nine thousand, five hundred fifty-seven".