21071666 has 36 divisors (see below), whose sum is σ = 40437054. Its totient is φ = 8205120.

The previous prime is 21071647. The next prime is 21071683. The reversal of 21071666 is 66617012.

It can be written as a sum of positive squares in only one way, i.e., 17935225 + 3136441 = 4235^2 + 1771^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 10970 + ... + 12746.

Almost surely, 2^21071666 is an apocalyptic number.

21071666 is a deficient number, since it is larger than the sum of its proper divisors (19365388).

21071666 is a wasteful number, since it uses less digits than its factorization.

21071666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1815 (or 1797 counting only the distinct ones).

The product of its (nonzero) digits is 3024, while the sum is 29.

The square root of 21071666 is about 4590.3884367230. The cubic root of 21071666 is about 276.2059042521.

Adding to 21071666 its reverse (66617012), we get a palindrome (87688678).

It can be divided in two parts, 2107 and 1666, that added together give a palindrome (3773).

The spelling of 21071666 in words is "twenty-one million, seventy-one thousand, six hundred sixty-six".