208128921 has 48 divisors (see below), whose sum is σ = 379286208. Its totient is φ = 99792000.

The previous prime is 208128919. The next prime is 208128953. The reversal of 208128921 is 129821802.

It is not a de Polignac number, because 208128921 - 2¹ = 208128919 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is not an unprimeable number, because it can be changed into a prime (208128971) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 16071 + ... + 25971.

It is an arithmetic number, because the mean of its divisors is an integer number (7901796).

Almost surely, 2^208128921 is an apocalyptic number.

208128921 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

208128921 is a deficient number, since it is larger than the sum of its proper divisors (171157287).

208128921 is a wasteful number, since it uses less digits than its factorization.

208128921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9942 (or 9935 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 33.

The square root of 208128921 is about 14426.6739410025. The cubic root of 208128921 is about 592.6216012055.

The spelling of 208128921 in words is "two hundred eight million, one hundred twenty-eight thousand, nine hundred twenty-one".