1851555421 has 2 divisors, whose sum is σ = 1851555422. Its totient is φ = 1851555420.

The previous prime is 1851555403. The next prime is 1851555439. The reversal of 1851555421 is 1245551581.

It is a balanced prime because it is at equal distance from previous prime (1851555403) and next prime (1851555439).

It can be written as a sum of positive squares in only one way, i.e., 1670356900 + 181198521 = 40870^2 + 13461^2 .

It is an emirp because it is prime and its reverse (1245551581) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1851555421 - 2⁵ = 1851555389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1851555401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 925777710 + 925777711.

It is an arithmetic number, because the mean of its divisors is an integer number (925777711).

Almost surely, 2^1851555421 is an apocalyptic number.

It is an amenable number.

1851555421 is a deficient number, since it is larger than the sum of its proper divisors (1).

1851555421 is an equidigital number, since it uses as much as digits as its factorization.

1851555421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 40000, while the sum is 37.

The square root of 1851555421 is about 43029.7039380937. The cubic root of 1851555421 is about 1227.9449724146.

The spelling of 1851555421 in words is "one billion, eight hundred fifty-one million, five hundred fifty-five thousand, four hundred twenty-one".