1921865805 has 32 divisors (see below), whose sum is σ = 3421180800. Its totient is φ = 1023636096.

The previous prime is 1921865741. The next prime is 1921865819. The reversal of 1921865805 is 5085681291.

It is a happy number.

It is not a de Polignac number, because 1921865805 - 2⁶ = 1921865741 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 97201 + ... + 115289.

It is an arithmetic number, because the mean of its divisors is an integer number (106911900).

Almost surely, 2^1921865805 is an apocalyptic number.

1921865805 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1921865805 is a deficient number, since it is larger than the sum of its proper divisors (1499314995).

1921865805 is a wasteful number, since it uses less digits than its factorization.

1921865805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18890 (or 18884 counting only the distinct ones).

The product of its (nonzero) digits is 172800, while the sum is 45.

The square root of 1921865805 is about 43839.0899198421. The cubic root of 1921865805 is about 1243.2954755072.

The spelling of 1921865805 in words is "one billion, nine hundred twenty-one million, eight hundred sixty-five thousand, eight hundred five".