2181917521 has 9 divisors (see below), whose sum is σ = 2538529371. Its totient is φ = 1869934752.

The previous prime is 2181917501. The next prime is 2181917537. The reversal of 2181917521 is 1257191812.

The square root of 2181917521 is 46711.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 78411025 + 2103506496 = 8855^2 + 45864^2 .

It is not a de Polignac number, because 2181917521 - 2⁵ = 2181917489 is a prime.

It is not an unprimeable number, because it can be changed into a prime (2181917501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 323641 + ... + 330313.

It is an arithmetic number, because the mean of its divisors is an integer number (282058819).

Almost surely, 2^2181917521 is an apocalyptic number.

2181917521 is the 46711-st square number.

2181917521 is the 23356-th centered octagonal number.

It is an amenable number.

2181917521 is a deficient number, since it is larger than the sum of its proper divisors (356611850).

2181917521 is an frugal number, since it uses more digits than its factorization.

2181917521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13360 (or 6680 counting only the distinct ones).

The product of its digits is 10080, while the sum is 37.

The cubic root of 2181917521 is about 1297.0183185114.

It can be divided in two parts, 21819 and 17521, that added together give a triangular number (39340 = T₂₈₀).

The spelling of 2181917521 in words is "two billion, one hundred eighty-one million, nine hundred seventeen thousand, five hundred twenty-one".