21681451 has 16 divisors (see below), whose sum is σ = 25061760. Its totient is φ = 18550080.

The previous prime is 21681449. The next prime is 21681467. The reversal of 21681451 is 15418612.

It is not a de Polignac number, because 21681451 - 2¹ = 21681449 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21681421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 47215 + ... + 47671.

It is an arithmetic number, because the mean of its divisors is an integer number (1566360).

Almost surely, 2^21681451 is an apocalyptic number.

21681451 is a deficient number, since it is larger than the sum of its proper divisors (3380309).

21681451 is a wasteful number, since it uses less digits than its factorization.

21681451 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 714.

The product of its digits is 1920, while the sum is 28.

The square root of 21681451 is about 4656.3345025889. The cubic root of 21681451 is about 278.8449483837.

It can be divided in two parts, 21 and 681451, that added together give a cube (681472 = 88³).

The spelling of 21681451 in words is "twenty-one million, six hundred eighty-one thousand, four hundred fifty-one".