21666051 has 12 divisors (see below), whose sum is σ = 34140600. Its totient is φ = 13130880.

The previous prime is 21666049. The next prime is 21666059. The reversal of 21666051 is 15066612.

It is a happy number.

It is not a de Polignac number, because 21666051 - 2¹ = 21666049 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21666059) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 109326 + ... + 109523.

It is an arithmetic number, because the mean of its divisors is an integer number (2845050).

Almost surely, 2^21666051 is an apocalyptic number.

21666051 is a deficient number, since it is larger than the sum of its proper divisors (12474549).

21666051 is a wasteful number, since it uses less digits than its factorization.

21666051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 218866 (or 218863 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21666051 is about 4654.6805475779. The cubic root of 21666051 is about 278.7789129923.

The spelling of 21666051 in words is "twenty-one million, six hundred sixty-six thousand, fifty-one".