13781666 has 4 divisors (see below), whose sum is σ = 20672502. Its totient is φ = 6890832.

The previous prime is 13781653. The next prime is 13781681. The reversal of 13781666 is 66618731.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66618731 = 19 ⋅3506249.

It can be written as a sum of positive squares in only one way, i.e., 11363641 + 2418025 = 3371^2 + 1555^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3445415 + ... + 3445418.

Almost surely, 2^13781666 is an apocalyptic number.

13781666 is a deficient number, since it is larger than the sum of its proper divisors (6890836).

13781666 is an equidigital number, since it uses as much as digits as its factorization.

13781666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6890835.

The product of its digits is 36288, while the sum is 38.

The square root of 13781666 is about 3712.3666306010. The cubic root of 13781666 is about 239.7547610672.

The spelling of 13781666 in words is "thirteen million, seven hundred eighty-one thousand, six hundred sixty-six".