1621521521 has 4 divisors (see below), whose sum is σ = 1621939200. Its totient is φ = 1621103844.

The previous prime is 1621521493. The next prime is 1621521547. The reversal of 1621521521 is 1251251261.

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: 1251251261 = 13 ⋅96250097.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1621521521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1621521571) 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, 202961 + ... + 210798.

It is an arithmetic number, because the mean of its divisors is an integer number (405484800).

Almost surely, 2^1621521521 is an apocalyptic number.

It is an amenable number.

1621521521 is a deficient number, since it is larger than the sum of its proper divisors (417679).

1621521521 is an equidigital number, since it uses as much as digits as its factorization.

1621521521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 417678.

The product of its digits is 1200, while the sum is 26.

The square root of 1621521521 is about 40268.1204056013. The cubic root of 1621521521 is about 1174.8278657754.

Adding to 1621521521 its reverse (1251251261), we get a palindrome (2872772782).

The spelling of 1621521521 in words is "one billion, six hundred twenty-one million, five hundred twenty-one thousand, five hundred twenty-one".