128721639 has 16 divisors (see below), whose sum is σ = 179730432. Its totient is φ = 81790368.

The previous prime is 128721617. The next prime is 128721643. The reversal of 128721639 is 936127821.

It is not a de Polignac number, because 128721639 - 2¹³ = 128713447 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 128721597 and 128721606.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128721139) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17034 + ... + 23400.

It is an arithmetic number, because the mean of its divisors is an integer number (11233152).

Almost surely, 2^128721639 is an apocalyptic number.

128721639 is a deficient number, since it is larger than the sum of its proper divisors (51008793).

128721639 is a wasteful number, since it uses less digits than its factorization.

128721639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6686.

The product of its digits is 36288, while the sum is 39.

The square root of 128721639 is about 11345.5559141013. Note that the first 3 decimals coincide. The cubic root of 128721639 is about 504.9137375123.

The spelling of 128721639 in words is "one hundred twenty-eight million, seven hundred twenty-one thousand, six hundred thirty-nine".