1661691406 has 4 divisors (see below), whose sum is σ = 2492537112. Its totient is φ = 830845702.

The previous prime is 1661691391. The next prime is 1661691407. The reversal of 1661691406 is 6041961661.

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

It is a super-2 number, since 2×1661691406² = 5522436657548513672, which contains 22 as substring.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661691407) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 415422850 + ... + 415422853.

It is an arithmetic number, because the mean of its divisors is an integer number (623134278).

Almost surely, 2^1661691406 is an apocalyptic number.

1661691406 is a deficient number, since it is larger than the sum of its proper divisors (830845706).

1661691406 is an equidigital number, since it uses as much as digits as its factorization.

1661691406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 830845705.

The product of its (nonzero) digits is 46656, while the sum is 40.

The square root of 1661691406 is about 40763.8492539652. The cubic root of 1661691406 is about 1184.4501608616.

The spelling of 1661691406 in words is "one billion, six hundred sixty-one million, six hundred ninety-one thousand, four hundred six".