21051647 has 8 divisors (see below), whose sum is σ = 22142976. Its totient is φ = 19975032.

The previous prime is 21051643. The next prime is 21051673. The reversal of 21051647 is 74615012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21051647 - 2² = 21051643 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 683 + ... + 6524.

It is an arithmetic number, because the mean of its divisors is an integer number (2767872).

Almost surely, 2^21051647 is an apocalyptic number.

21051647 is the 2453-rd centered heptagonal number.

21051647 is a deficient number, since it is larger than the sum of its proper divisors (1091329).

21051647 is a wasteful number, since it uses less digits than its factorization.

21051647 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7357.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 21051647 is about 4588.2073841534. The cubic root of 21051647 is about 276.1184073266.

Adding to 21051647 its reverse (74615012), we get a palindrome (95666659).

The spelling of 21051647 in words is "twenty-one million, fifty-one thousand, six hundred forty-seven".