129555821 has 2 divisors, whose sum is σ = 129555822. Its totient is φ = 129555820.

The previous prime is 129555817. The next prime is 129555857. The reversal of 129555821 is 128555921.

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., 94284100 + 35271721 = 9710^2 + 5939^2 .

It is a cyclic number.

It is not a de Polignac number, because 129555821 - 2² = 129555817 is a prime.

It is equal to p_7354496 and since 129555821 and 7354496 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (129555221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64777910 + 64777911.

It is an arithmetic number, because the mean of its divisors is an integer number (64777911).

Almost surely, 2^129555821 is an apocalyptic number.

It is an amenable number.

129555821 is a deficient number, since it is larger than the sum of its proper divisors (1).

129555821 is an equidigital number, since it uses as much as digits as its factorization.

129555821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36000, while the sum is 38.

The square root of 129555821 is about 11382.2590464283. The cubic root of 129555821 is about 506.0020895413.

The spelling of 129555821 in words is "one hundred twenty-nine million, five hundred fifty-five thousand, eight hundred twenty-one".