1821908561 has 4 divisors (see below), whose sum is σ = 1987536624. Its totient is φ = 1656280500.

The previous prime is 1821908519. The next prime is 1821908563. The reversal of 1821908561 is 1658091281.

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.

It is a cyclic number.

It is not a de Polignac number, because 1821908561 - 2¹⁰ = 1821907537 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (1821908563) 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, 82814015 + ... + 82814036.

It is an arithmetic number, because the mean of its divisors is an integer number (496884156).

Almost surely, 2^1821908561 is an apocalyptic number.

1821908561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1821908561 is a deficient number, since it is larger than the sum of its proper divisors (165628063).

1821908561 is a wasteful number, since it uses less digits than its factorization.

1821908561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 165628062.

The product of its (nonzero) digits is 34560, while the sum is 41.

The square root of 1821908561 is about 42683.8208341287. The cubic root of 1821908561 is about 1221.3557804607.

The spelling of 1821908561 in words is "one billion, eight hundred twenty-one million, nine hundred eight thousand, five hundred sixty-one".