16686421 has 4 divisors (see below), whose sum is σ = 16761472. Its totient is φ = 16611372.

The previous prime is 16686419. The next prime is 16686437. The reversal of 16686421 is 12468661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12468661 = 487 ⋅25603.

It is a cyclic number.

It is not a de Polignac number, because 16686421 - 2¹ = 16686419 is a prime.

It is a super-3 number, since 3×16686421³ (a number of 23 digits) contains 333 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 (16686821) 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, 37191 + ... + 37636.

It is an arithmetic number, because the mean of its divisors is an integer number (4190368).

Almost surely, 2^16686421 is an apocalyptic number.

It is an amenable number.

16686421 is a deficient number, since it is larger than the sum of its proper divisors (75051).

16686421 is an equidigital number, since it uses as much as digits as its factorization.

16686421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 75050.

The product of its digits is 13824, while the sum is 34.

The square root of 16686421 is about 4084.9015900019. The cubic root of 16686421 is about 255.5373571652.

The spelling of 16686421 in words is "sixteen million, six hundred eighty-six thousand, four hundred twenty-one".