21517651 has 4 divisors (see below), whose sum is σ = 21660304. Its totient is φ = 21375000.

The previous prime is 21517649. The next prime is 21517669. The reversal of 21517651 is 15671512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21517651 - 2¹ = 21517649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21517621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71100 + ... + 71401.

It is an arithmetic number, because the mean of its divisors is an integer number (5415076).

Almost surely, 2^21517651 is an apocalyptic number.

21517651 is a deficient number, since it is larger than the sum of its proper divisors (142653).

21517651 is a wasteful number, since it uses less digits than its factorization.

21517651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 142652.

The product of its digits is 2100, while the sum is 28.

The square root of 21517651 is about 4638.7122135351. The cubic root of 21517651 is about 278.1409624471.

The spelling of 21517651 in words is "twenty-one million, five hundred seventeen thousand, six hundred fifty-one".