21371661 has 8 divisors (see below), whose sum is σ = 31661760. Its totient is φ = 14247756.

The previous prime is 21371657. The next prime is 21371663. The reversal of 21371661 is 16617312.

It is not a de Polignac number, because 21371661 - 2² = 21371657 is a prime.

It is a super-3 number, since 3×21371661³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 791543 = 21371661 / (2 + 1 + 3 + 7 + 1 + 6 + 6 + 1).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21371663) 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, 395745 + ... + 395798.

It is an arithmetic number, because the mean of its divisors is an integer number (3957720).

Almost surely, 2^21371661 is an apocalyptic number.

It is an amenable number.

21371661 is a deficient number, since it is larger than the sum of its proper divisors (10290099).

21371661 is an equidigital number, since it uses as much as digits as its factorization.

21371661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 791552 (or 791546 counting only the distinct ones).

The product of its digits is 1512, while the sum is 27.

The square root of 21371661 is about 4622.9493832401. The cubic root of 21371661 is about 277.5105036200.

Adding to 21371661 its reverse (16617312), we get a palindrome (37988973).

The spelling of 21371661 in words is "twenty-one million, three hundred seventy-one thousand, six hundred sixty-one".