21651457 has 4 divisors (see below), whose sum is σ = 21662676. Its totient is φ = 21640240.

The previous prime is 21651449. The next prime is 21651473. The reversal of 21651457 is 75415612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7203856 + 14447601 = 2684^2 + 3801^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651457 - 2³ = 21651449 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21655457) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1894 + ... + 6847.

It is an arithmetic number, because the mean of its divisors is an integer number (5415669).

It is a Proth number, since it is equal to 2643 ⋅ 2¹³ + 1 and 2643 < 2¹³.

Almost surely, 2^21651457 is an apocalyptic number.

It is an amenable number.

21651457 is a deficient number, since it is larger than the sum of its proper divisors (11219).

21651457 is an equidigital number, since it uses as much as digits as its factorization.

21651457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11218.

The product of its digits is 8400, while the sum is 31.

The square root of 21651457 is about 4653.1126141541. The cubic root of 21651457 is about 278.7163048548.

The spelling of 21651457 in words is "twenty-one million, six hundred fifty-one thousand, four hundred fifty-seven".