16721661 has 32 divisors (see below), whose sum is σ = 25557120. Its totient is φ = 9632000.

The previous prime is 16721657. The next prime is 16721671. The reversal of 16721661 is 16612761.

It is a cyclic number.

It is not a de Polignac number, because 16721661 - 2² = 16721657 is a prime.

It is a super-2 number, since 2×16721661² = 559227893197842, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16721611) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 96571 + ... + 96743.

It is an arithmetic number, because the mean of its divisors is an integer number (798660).

Almost surely, 2^16721661 is an apocalyptic number.

16721661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

16721661 is a deficient number, since it is larger than the sum of its proper divisors (8835459).

16721661 is a wasteful number, since it uses less digits than its factorization.

16721661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 317.

The product of its digits is 3024, while the sum is 30.

The square root of 16721661 is about 4089.2127604222. The cubic root of 16721661 is about 255.7171201910.

Subtracting from 16721661 its reverse (16612761), we obtain a square (108900 = 330²).

It can be divided in two parts, 1672 and 1661, that added together give a palindrome (3333).

The spelling of 16721661 in words is "sixteen million, seven hundred twenty-one thousand, six hundred sixty-one".