21006736 has 10 divisors (see below), whose sum is σ = 40700582. Its totient is φ = 10503360.

The previous prime is 21006731. The next prime is 21006737. The reversal of 21006736 is 63760012.

It can be written as a sum of positive squares in only one way, i.e., 19891600 + 1115136 = 4460^2 + 1056^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21006736.

It is not an unprimeable number, because it can be changed into a prime (21006731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 656445 + ... + 656476.

Almost surely, 2^21006736 is an apocalyptic number.

It is an amenable number.

21006736 is a deficient number, since it is larger than the sum of its proper divisors (19693846).

21006736 is a wasteful number, since it uses less digits than its factorization.

21006736 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1312929 (or 1312923 counting only the distinct ones).

The product of its (nonzero) digits is 1512, while the sum is 25.

The square root of 21006736 is about 4583.3105938830. The cubic root of 21006736 is about 275.9219130771.

Adding to 21006736 its reverse (63760012), we get a palindrome (84766748).

It can be divided in two parts, 2100 and 6736, that added together give a square (8836 = 94²).

The spelling of 21006736 in words is "twenty-one million, six thousand, seven hundred thirty-six".