7905128921 has 4 divisors (see below), whose sum is σ = 8118781092. Its totient is φ = 7691476752.

The previous prime is 7905128899. The next prime is 7905128947. The reversal of 7905128921 is 1298215097.

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 7295038921 + 610090000 = 85411^2 + 24700^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7905128921 is a prime.

It is not an unprimeable number, because it can be changed into a prime (7905128521) 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, 106826030 + ... + 106826103.

It is an arithmetic number, because the mean of its divisors is an integer number (2029695273).

Almost surely, 2^7905128921 is an apocalyptic number.

It is an amenable number.

7905128921 is a deficient number, since it is larger than the sum of its proper divisors (213652171).

7905128921 is a wasteful number, since it uses less digits than its factorization.

7905128921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213652170.

The product of its (nonzero) digits is 90720, while the sum is 44.

The square root of 7905128921 is about 88910.7919265147. The cubic root of 7905128921 is about 1992.0626174014.

The spelling of 7905128921 in words is "seven billion, nine hundred five million, one hundred twenty-eight thousand, nine hundred twenty-one".