128917921 has 8 divisors (see below), whose sum is σ = 146752704. Its totient is φ = 112102320.

The previous prime is 128917903. The next prime is 128917939. The reversal of 128917921 is 129719821.

It is an interprime number because it is at equal distance from previous prime (128917903) and next prime (128917939).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 128917921 - 2¹¹ = 128915873 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128917121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 254526 + ... + 255031.

It is an arithmetic number, because the mean of its divisors is an integer number (18344088).

Almost surely, 2^128917921 is an apocalyptic number.

128917921 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

128917921 is a deficient number, since it is larger than the sum of its proper divisors (17834783).

128917921 is a wasteful number, since it uses less digits than its factorization.

128917921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 509591.

The product of its digits is 18144, while the sum is 40.

The square root of 128917921 is about 11354.2027901566. The cubic root of 128917921 is about 505.1702474712.

The spelling of 128917921 in words is "one hundred twenty-eight million, nine hundred seventeen thousand, nine hundred twenty-one".