129126021 has 4 divisors (see below), whose sum is σ = 172168032. Its totient is φ = 86084012.

The previous prime is 129126017. The next prime is 129126047. The reversal of 129126021 is 120621921.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 129126021 - 2² = 129126017 is a prime.

It is a super-3 number, since 3×129126021³ (a number of 25 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 129125982 and 129126000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (129126091) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21521001 + ... + 21521006.

It is an arithmetic number, because the mean of its divisors is an integer number (43042008).

Almost surely, 2^129126021 is an apocalyptic number.

It is an amenable number.

129126021 is a deficient number, since it is larger than the sum of its proper divisors (43042011).

129126021 is an equidigital number, since it uses as much as digits as its factorization.

129126021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 43042010.

The product of its (nonzero) digits is 432, while the sum is 24.

The square root of 129126021 is about 11363.3631025326. The cubic root of 129126021 is about 505.4419175214.

Adding to 129126021 its reverse (120621921), we get a palindrome (249747942).

The spelling of 129126021 in words is "one hundred twenty-nine million, one hundred twenty-six thousand, twenty-one".