1661656391 has 4 divisors (see below), whose sum is σ = 1663411992. Its totient is φ = 1659900792.

The previous prime is 1661656387. The next prime is 1661656411. The reversal of 1661656391 is 1936561661.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1661656391 - 2² = 1661656387 is a prime.

It is a super-2 number, since 2×1661656391² = 5522203923502289762, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661656991) 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, 876380 + ... + 878273.

It is an arithmetic number, because the mean of its divisors is an integer number (415852998).

Almost surely, 2^1661656391 is an apocalyptic number.

1661656391 is a deficient number, since it is larger than the sum of its proper divisors (1755601).

1661656391 is an equidigital number, since it uses as much as digits as its factorization.

1661656391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1755600.

The product of its digits is 174960, while the sum is 44.

The square root of 1661656391 is about 40763.4197657655. The cubic root of 1661656391 is about 1184.4418412636.

The spelling of 1661656391 in words is "one billion, six hundred sixty-one million, six hundred fifty-six thousand, three hundred ninety-one".