1556721421 has 4 divisors (see below), whose sum is σ = 1610401500. Its totient is φ = 1503041344.

The previous prime is 1556721409. The next prime is 1556721427. The reversal of 1556721421 is 1241276551.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1241276551 = 2969 ⋅418079.

It can be written as a sum of positive squares in 2 ways, for example, as 887205796 + 669515625 = 29786^2 + 25875^2 .

It is a cyclic number.

It is not a de Polignac number, because 1556721421 - 2¹⁷ = 1556590349 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 (1556721427) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26839996 + ... + 26840053.

It is an arithmetic number, because the mean of its divisors is an integer number (402600375).

Almost surely, 2^1556721421 is an apocalyptic number.

It is an amenable number.

1556721421 is a deficient number, since it is larger than the sum of its proper divisors (53680079).

1556721421 is an equidigital number, since it uses as much as digits as its factorization.

1556721421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53680078.

The product of its digits is 16800, while the sum is 34.

The square root of 1556721421 is about 39455.3091611256. The cubic root of 1556721421 is about 1158.9649459613.

Adding to 1556721421 its reverse (1241276551), we get a palindrome (2797997972).

The spelling of 1556721421 in words is "one billion, five hundred fifty-six million, seven hundred twenty-one thousand, four hundred twenty-one".