21621745 has 8 divisors (see below), whose sum is σ = 25971840. Its totient is φ = 17280240.

The previous prime is 21621737. The next prime is 21621757. The reversal of 21621745 is 54712612.

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

It is not a de Polignac number, because 21621745 - 2³ = 21621737 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6760 + ... + 9430.

It is an arithmetic number, because the mean of its divisors is an integer number (3246480).

Almost surely, 2^21621745 is an apocalyptic number.

It is an amenable number.

21621745 is a deficient number, since it is larger than the sum of its proper divisors (4350095).

21621745 is a wasteful number, since it uses less digits than its factorization.

21621745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4295.

The product of its digits is 3360, while the sum is 28.

The square root of 21621745 is about 4649.9188164956. The cubic root of 21621745 is about 278.5887536265.

It can be divided in two parts, 21621 and 745, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21621745 in words is "twenty-one million, six hundred twenty-one thousand, seven hundred forty-five".