1991643543975 has 24 divisors (see below), whose sum is σ = 3354979923792. Its totient is φ = 1042168192000.

The previous prime is 1991643543959. The next prime is 1991643544039. The reversal of 1991643543975 is 5793453461991.

It is not a de Polignac number, because 1991643543975 - 2⁴ = 1991643543959 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 250517226 + ... + 250525175.

It is an arithmetic number, because the mean of its divisors is an integer number (139790830158).

Almost surely, 2^{1991643543975} is an apocalyptic number.

1991643543975 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1991643543975 is a deficient number, since it is larger than the sum of its proper divisors (1363336379817).

1991643543975 is a wasteful number, since it uses less digits than its factorization.

1991643543975 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 501042467 (or 501042462 counting only the distinct ones).

The product of its digits is 110224800, while the sum is 66.

The spelling of 1991643543975 in words is "one trillion, nine hundred ninety-one billion, six hundred forty-three million, five hundred forty-three thousand, nine hundred seventy-five".