1555657421 has 4 divisors (see below), whose sum is σ = 1558308192. Its totient is φ = 1553006652.

The previous prime is 1555657409. The next prime is 1555657427. The reversal of 1555657421 is 1247565551.

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: 1247565551 = 79 ⋅15791969.

It is a cyclic number.

It is not a de Polignac number, because 1555657421 - 2¹⁴ = 1555641037 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 (1555657427) 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, 1324505 + ... + 1325678.

It is an arithmetic number, because the mean of its divisors is an integer number (389577048).

Almost surely, 2^1555657421 is an apocalyptic number.

It is an amenable number.

1555657421 is a deficient number, since it is larger than the sum of its proper divisors (2650771).

1555657421 is an equidigital number, since it uses as much as digits as its factorization.

1555657421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2650770.

The product of its digits is 210000, while the sum is 41.

The square root of 1555657421 is about 39441.8232463967. The cubic root of 1555657421 is about 1158.7008396719.

The spelling of 1555657421 in words is "one billion, five hundred fifty-five million, six hundred fifty-seven thousand, four hundred twenty-one".