81658909 has 2 divisors, whose sum is σ = 81658910. Its totient is φ = 81658908.

The previous prime is 81658859. The next prime is 81658949. The reversal of 81658909 is 90985618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 49702500 + 31956409 = 7050^2 + 5653^2 .

It is a cyclic number.

It is not a de Polignac number, because 81658909 - 2⁷ = 81658781 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81658949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40829454 + 40829455.

It is an arithmetic number, because the mean of its divisors is an integer number (40829455).

Almost surely, 2^81658909 is an apocalyptic number.

It is an amenable number.

81658909 is a deficient number, since it is larger than the sum of its proper divisors (1).

81658909 is an equidigital number, since it uses as much as digits as its factorization.

81658909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 155520, while the sum is 46.

The square root of 81658909 is about 9036.5319121884. The cubic root of 81658909 is about 433.8449278566.

The spelling of 81658909 in words is "eighty-one million, six hundred fifty-eight thousand, nine hundred nine".