128691421 has 4 divisors (see below), whose sum is σ = 128742172. Its totient is φ = 128640672.

The previous prime is 128691401. The next prime is 128691443. The reversal of 128691421 is 124196821.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 42758521 + 85932900 = 6539^2 + 9270^2 .

It is a cyclic number.

It is not a de Polignac number, because 128691421 - 2⁹ = 128690909 is a prime.

It is a super-2 number, since 2×128691421² = 33122963677998482, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128691401) 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, 21360 + ... + 26713.

It is an arithmetic number, because the mean of its divisors is an integer number (32185543).

Almost surely, 2^128691421 is an apocalyptic number.

It is an amenable number.

128691421 is a deficient number, since it is larger than the sum of its proper divisors (50751).

128691421 is an equidigital number, since it uses as much as digits as its factorization.

128691421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50750.

The product of its digits is 6912, while the sum is 34.

The square root of 128691421 is about 11344.2241250779. The cubic root of 128691421 is about 504.8742241419.

The spelling of 128691421 in words is "one hundred twenty-eight million, six hundred ninety-one thousand, four hundred twenty-one".