21009651 has 8 divisors (see below), whose sum is σ = 30167760. Its totient is φ = 12928992.

The previous prime is 21009643. The next prime is 21009679. The reversal of 21009651 is 15690012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21009651 - 2³ = 21009643 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21009691) 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 7 ways as a sum of consecutive naturals, for example, 269316 + ... + 269393.

It is an arithmetic number, because the mean of its divisors is an integer number (3770970).

Almost surely, 2^21009651 is an apocalyptic number.

21009651 is a deficient number, since it is larger than the sum of its proper divisors (9158109).

21009651 is a wasteful number, since it uses less digits than its factorization.

21009651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 538725.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21009651 is about 4583.6285844296. The cubic root of 21009651 is about 275.9346752561.

Adding to 21009651 its reverse (15690012), we get a palindrome (36699663).

The spelling of 21009651 in words is "twenty-one million, nine thousand, six hundred fifty-one".