1521204221 has 4 divisors (see below), whose sum is σ = 1524835200. Its totient is φ = 1517573244.

The previous prime is 1521204161. The next prime is 1521204229. The reversal of 1521204221 is 1224021251.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1224021251 = 151 ⋅8106101.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1521204221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1521204193 and 1521204202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1521204229) 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, 1814861 + ... + 1815698.

It is an arithmetic number, because the mean of its divisors is an integer number (381208800).

Almost surely, 2^1521204221 is an apocalyptic number.

It is an amenable number.

1521204221 is a deficient number, since it is larger than the sum of its proper divisors (3630979).

1521204221 is an equidigital number, since it uses as much as digits as its factorization.

1521204221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3630978.

The product of its (nonzero) digits is 320, while the sum is 20.

The square root of 1521204221 is about 39002.6181300692. The cubic root of 1521204221 is about 1150.0829734713.

Adding to 1521204221 its reverse (1224021251), we get a palindrome (2745225472).

The spelling of 1521204221 in words is "one billion, five hundred twenty-one million, two hundred four thousand, two hundred twenty-one".