1815815381 has 2 divisors, whose sum is σ = 1815815382. Its totient is φ = 1815815380.

The previous prime is 1815815369. The next prime is 1815815401. The reversal of 1815815381 is 1835185181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1800644356 + 15171025 = 42434^2 + 3895^2 .

It is an emirp because it is prime and its reverse (1835185181) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1815815381 - 2¹⁸ = 1815553237 is a prime.

It is a super-2 number, since 2×1815815381² = 6594370995752350322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1815815341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 907907690 + 907907691.

It is an arithmetic number, because the mean of its divisors is an integer number (907907691).

Almost surely, 2^1815815381 is an apocalyptic number.

It is an amenable number.

1815815381 is a deficient number, since it is larger than the sum of its proper divisors (1).

1815815381 is an equidigital number, since it uses as much as digits as its factorization.

1815815381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 38400, while the sum is 41.

The square root of 1815815381 is about 42612.3853005203. The cubic root of 1815815381 is about 1219.9926947964.

The spelling of 1815815381 in words is "one billion, eight hundred fifteen million, eight hundred fifteen thousand, three hundred eighty-one".