81820121 has 2 divisors, whose sum is σ = 81820122. Its totient is φ = 81820120.

The previous prime is 81820117. The next prime is 81820153. The reversal of 81820121 is 12102818.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50055625 + 31764496 = 7075^2 + 5636^2 .

It is a cyclic number.

It is not a de Polignac number, because 81820121 - 2² = 81820117 is a prime.

It is not a weakly prime, because it can be changed into another prime (81820021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40910060 + 40910061.

It is an arithmetic number, because the mean of its divisors is an integer number (40910061).

Almost surely, 2^81820121 is an apocalyptic number.

It is an amenable number.

81820121 is a deficient number, since it is larger than the sum of its proper divisors (1).

81820121 is an equidigital number, since it uses as much as digits as its factorization.

81820121 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 256, while the sum is 23.

The square root of 81820121 is about 9045.4475290060. The cubic root of 81820121 is about 434.1302408071.

Adding to 81820121 its reverse (12102818), we get a palindrome (93922939).

The spelling of 81820121 in words is "eighty-one million, eight hundred twenty thousand, one hundred twenty-one".