1815819221 has 2 divisors, whose sum is σ = 1815819222. Its totient is φ = 1815819220.

The previous prime is 1815819209. The next prime is 1815819259. The reversal of 1815819221 is 1229185181.

It is an a-pointer prime, because the next prime (1815819259) can be obtained adding 1815819221 to its sum of digits (38).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1445064196 + 370755025 = 38014^2 + 19255^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1815819221 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1815849221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 907909610 + 907909611.

It is an arithmetic number, because the mean of its divisors is an integer number (907909611).

Almost surely, 2^1815819221 is an apocalyptic number.

It is an amenable number.

1815819221 is a deficient number, since it is larger than the sum of its proper divisors (1).

1815819221 is an equidigital number, since it uses as much as digits as its factorization.

1815819221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11520, while the sum is 38.

The square root of 1815819221 is about 42612.4303578193. The cubic root of 1815819221 is about 1219.9935547899.

The spelling of 1815819221 in words is "one billion, eight hundred fifteen million, eight hundred nineteen thousand, two hundred twenty-one".