1561628821 has 4 divisors (see below), whose sum is σ = 1562391532. Its totient is φ = 1560866112.

The previous prime is 1561628759. The next prime is 1561628839. The reversal of 1561628821 is 1288261651.

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 1174090225 + 387538596 = 34265^2 + 19686^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561628821 - 2¹⁵ = 1561596053 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1561628521) 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 3 ways as a sum of consecutive naturals, for example, 378276 + ... + 382381.

It is an arithmetic number, because the mean of its divisors is an integer number (390597883).

Almost surely, 2^1561628821 is an apocalyptic number.

It is an amenable number.

1561628821 is a deficient number, since it is larger than the sum of its proper divisors (762711).

1561628821 is an equidigital number, since it uses as much as digits as its factorization.

1561628821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 762710.

The product of its digits is 46080, while the sum is 40.

The square root of 1561628821 is about 39517.4495761050. The cubic root of 1561628821 is about 1160.1815067248.

The spelling of 1561628821 in words is "one billion, five hundred sixty-one million, six hundred twenty-eight thousand, eight hundred twenty-one".