1661521 has 3 divisors (see below), whose sum is σ = 1662811.
Its totient is φ = 1660232.
The previous prime is 1661519. The next prime is 1661549. The reversal of 1661521 is 1251661.
The square root of 1661521 is 1289.
It is a perfect power (a square), and thus also a powerful number.
It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.
It can be written as a sum of positive squares in only one way, i.e., 1347921 + 313600 = 1161^2 + 560^2
It is not a de Polignac number, because 1661521 - 21 = 1661519 is a prime.
It is a Duffinian number.
1661521 is a lucky number.
It is a junction number, because it is equal to n+sod(n) for n = 1661492 and 1661501.
It is not an unprimeable number, because it can be changed into a prime (1661021) by changing a digit.
It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 645 + ... + 1933.
21661521 is an apocalyptic number.
1661521 is the 1289-th square number.
1661521 is the 645-th centered octagonal number.
It is an amenable number.
1661521 is a deficient number, since it is larger than the sum of its proper divisors (1290).
1661521 is an frugal number, since it uses more digits than its factorization.
1661521 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 2578 (or 1289 counting only the distinct ones).
The product of its digits is 360, while the sum is 22.
The cubic root of 1661521 is about 118.4409671131.
The spelling of 1661521 in words is "one million, six hundred sixty-one thousand, five hundred twenty-one".