21651451 has 4 divisors (see below), whose sum is σ = 21925600. Its totient is φ = 21377304.

The previous prime is 21651449. The next prime is 21651473. The reversal of 21651451 is 15415612.

It is a happy number.

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 21651451 - 2¹ = 21651449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21651491) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 136956 + ... + 137113.

It is an arithmetic number, because the mean of its divisors is an integer number (5481400).

Almost surely, 2^21651451 is an apocalyptic number.

21651451 is a deficient number, since it is larger than the sum of its proper divisors (274149).

21651451 is an equidigital number, since it uses as much as digits as its factorization.

21651451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 274148.

The product of its digits is 1200, while the sum is 25.

The square root of 21651451 is about 4653.1119694243. Note that the first 3 decimals coincide. The cubic root of 21651451 is about 278.7162791091.

The spelling of 21651451 in words is "twenty-one million, six hundred fifty-one thousand, four hundred fifty-one".