81987817 has 2 divisors, whose sum is σ = 81987818. Its totient is φ = 81987816.

The previous prime is 81987811. The next prime is 81987853. The reversal of 81987817 is 71878918.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77369616 + 4618201 = 8796^2 + 2149^2 .

It is a cyclic number.

It is not a de Polignac number, because 81987817 - 2³ = 81987809 is a prime.

It is not a weakly prime, because it can be changed into another prime (81987811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40993908 + 40993909.

It is an arithmetic number, because the mean of its divisors is an integer number (40993909).

Almost surely, 2^81987817 is an apocalyptic number.

It is an amenable number.

81987817 is a deficient number, since it is larger than the sum of its proper divisors (1).

81987817 is an equidigital number, since it uses as much as digits as its factorization.

81987817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 225792, while the sum is 49.

The square root of 81987817 is about 9054.7124195084. The cubic root of 81987817 is about 434.4266317316.

The spelling of 81987817 in words is "eighty-one million, nine hundred eighty-seven thousand, eight hundred seventeen".