21661505 has 8 divisors (see below), whose sum is σ = 26193024. Its totient is φ = 17196400.

The previous prime is 21661499. The next prime is 21661517. The reversal of 21661505 is 50516612.

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

It is a de Polignac number, because none of the positive numbers 2^k-21661505 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 11.

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, 15881 + ... + 17190.

It is an arithmetic number, because the mean of its divisors is an integer number (3274128).

Almost surely, 2^21661505 is an apocalyptic number.

It is an amenable number.

21661505 is a deficient number, since it is larger than the sum of its proper divisors (4531519).

21661505 is a wasteful number, since it uses less digits than its factorization.

21661505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33207.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21661505 is about 4654.1921962893. The cubic root of 21661505 is about 278.7594137061.

The spelling of 21661505 in words is "twenty-one million, six hundred sixty-one thousand, five hundred five".