21006256 has 10 divisors (see below), whose sum is σ = 40699652. Its totient is φ = 10503120.

The previous prime is 21006247. The next prime is 21006257. The reversal of 21006256 is 65260012.

It is a super-2 number, since 2×21006256² = 882525582275072, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21006257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 656430 + ... + 656461.

Almost surely, 2^21006256 is an apocalyptic number.

It is an amenable number.

21006256 is a deficient number, since it is larger than the sum of its proper divisors (19693396).

21006256 is a wasteful number, since it uses less digits than its factorization.

21006256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1312899 (or 1312893 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 22.

The square root of 21006256 is about 4583.2582296877. The cubic root of 21006256 is about 275.9198114730.

Adding to 21006256 its reverse (65260012), we get a palindrome (86266268).

The spelling of 21006256 in words is "twenty-one million, six thousand, two hundred fifty-six".