1661667191 has 2 divisors, whose sum is σ = 1661667192. Its totient is φ = 1661667190.

The previous prime is 1661667181. The next prime is 1661667247. The reversal of 1661667191 is 1917661661.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1661667191 is a prime.

It is a super-2 number, since 2×1661667191² = 5522275707291660962, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1661667121) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 830833595 + 830833596.

It is an arithmetic number, because the mean of its divisors is an integer number (830833596).

Almost surely, 2^1661667191 is an apocalyptic number.

1661667191 is a deficient number, since it is larger than the sum of its proper divisors (1).

1661667191 is an equidigital number, since it uses as much as digits as its factorization.

1661667191 is an evil number, because the sum of its binary digits is even.

The product of its digits is 81648, while the sum is 44.

The square root of 1661667191 is about 40763.5522372621. The cubic root of 1661667191 is about 1184.4444073665. Note that the first 4 decimals are identical.

The spelling of 1661667191 in words is "one billion, six hundred sixty-one million, six hundred sixty-seven thousand, one hundred ninety-one".