1991185531 has 2 divisors, whose sum is σ = 1991185532. Its totient is φ = 1991185530.

The previous prime is 1991185523. The next prime is 1991185561. The reversal of 1991185531 is 1355811991.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1991185531 - 2³ = 1991185523 is a prime.

It is a super-2 number, since 2×1991185531² = 7929639637727503922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1991185561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995592765 + 995592766.

It is an arithmetic number, because the mean of its divisors is an integer number (995592766).

Almost surely, 2^1991185531 is an apocalyptic number.

1991185531 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991185531 is an equidigital number, since it uses as much as digits as its factorization.

1991185531 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 48600, while the sum is 43.

The square root of 1991185531 is about 44622.7019688409. The cubic root of 1991185531 is about 1258.0674015615.

The spelling of 1991185531 in words is "one billion, nine hundred ninety-one million, one hundred eighty-five thousand, five hundred thirty-one".