21006510 has 64 divisors (see below), whose sum is σ = 58516992. Its totient is φ = 4726656.

The previous prime is 21006493. The next prime is 21006511. The reversal of 21006510 is 1560012.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21006510.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006511) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 13324 + ... + 14816.

It is an arithmetic number, because the mean of its divisors is an integer number (914328).

Almost surely, 2^21006510 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21006510, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29258496).

21006510 is an abundant number, since it is smaller than the sum of its proper divisors (37510482).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21006510 is a wasteful number, since it uses less digits than its factorization.

21006510 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1577.

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21006510 is about 4583.2859391489. The cubic root of 21006510 is about 275.9209235759.

Adding to 21006510 its reverse (1560012), we get a palindrome (22566522).

The spelling of 21006510 in words is "twenty-one million, six thousand, five hundred ten".