21661601 has 8 divisors (see below), whose sum is σ = 23370984. Its totient is φ = 19958400.

The previous prime is 21661597. The next prime is 21661609. The reversal of 21661601 is 10616612.

It can be written as a sum of positive squares in 4 ways, for example, as 2512225 + 19149376 = 1585^2 + 4376^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21661601 - 2² = 21661597 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21661609) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7925 + ... + 10301.

It is an arithmetic number, because the mean of its divisors is an integer number (2921373).

Almost surely, 2^21661601 is an apocalyptic number.

It is an amenable number.

21661601 is a deficient number, since it is larger than the sum of its proper divisors (1709383).

21661601 is a wasteful number, since it uses less digits than its factorization.

21661601 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3091.

The product of its (nonzero) digits is 432, while the sum is 23.

The square root of 21661601 is about 4654.2025095606. The cubic root of 21661601 is about 278.7598255098.

The spelling of 21661601 in words is "twenty-one million, six hundred sixty-one thousand, six hundred one".