21451661 has 12 divisors (see below), whose sum is σ = 27223200. Its totient is φ = 16715160.

The previous prime is 21451649. The next prime is 21451669. The reversal of 21451661 is 16615412.

It is a de Polignac number, because none of the positive numbers 2^k-21451661 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21451661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21451669) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 19361 + ... + 20438.

It is an arithmetic number, because the mean of its divisors is an integer number (2268600).

Almost surely, 2^21451661 is an apocalyptic number.

It is an amenable number.

21451661 is a deficient number, since it is larger than the sum of its proper divisors (5771539).

21451661 is a wasteful number, since it uses less digits than its factorization.

21451661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39824 (or 39817 counting only the distinct ones).

The product of its digits is 1440, while the sum is 26.

The square root of 21451661 is about 4631.5937861604. The cubic root of 21451661 is about 277.8563384847.

The spelling of 21451661 in words is "twenty-one million, four hundred fifty-one thousand, six hundred sixty-one".