21006513 has 16 divisors (see below), whose sum is σ = 33950400. Its totient is φ = 12731040.

The previous prime is 21006511. The next prime is 21006523. The reversal of 21006513 is 31560012.

21006513 is a `hidden beast` number, since 2 + 10 + 0 + 651 + 3 = 666.

It is not a de Polignac number, because 21006513 - 2¹ = 21006511 is a prime.

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 15 ways as a sum of consecutive naturals, for example, 35068 + ... + 35661.

It is an arithmetic number, because the mean of its divisors is an integer number (2121900).

Almost surely, 2^21006513 is an apocalyptic number.

It is an amenable number.

21006513 is a deficient number, since it is larger than the sum of its proper divisors (12943887).

21006513 is a wasteful number, since it uses less digits than its factorization.

21006513 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 70749 (or 70743 counting only the distinct ones).

The product of its (nonzero) digits is 180, while the sum is 18.

The square root of 21006513 is about 4583.2862664250. The cubic root of 21006513 is about 275.9209367109.

Adding to 21006513 its reverse (31560012), we get a palindrome (52566525).

The spelling of 21006513 in words is "twenty-one million, six thousand, five hundred thirteen".