128721365 has 16 divisors (see below), whose sum is σ = 166643568. Its totient is φ = 95087616.

The previous prime is 128721361. The next prime is 128721379. The reversal of 128721365 is 563127821.

It is a happy number.

It can be written as a sum of positive squares in 8 ways, for example, as 4153444 + 124567921 = 2038^2 + 11161^2 .

It is a cyclic number.

It is not a de Polignac number, because 128721365 - 2² = 128721361 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128721361) 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, 9782 + ... + 18791.

It is an arithmetic number, because the mean of its divisors is an integer number (10415223).

Almost surely, 2^128721365 is an apocalyptic number.

It is an amenable number.

128721365 is a deficient number, since it is larger than the sum of its proper divisors (37922203).

128721365 is a wasteful number, since it uses less digits than its factorization.

128721365 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 28648.

The product of its digits is 20160, while the sum is 35.

The square root of 128721365 is about 11345.5438388823. The cubic root of 128721365 is about 504.9133792548.

The spelling of 128721365 in words is "one hundred twenty-eight million, seven hundred twenty-one thousand, three hundred sixty-five".