21606506 has 4 divisors (see below), whose sum is σ = 32409762. Its totient is φ = 10803252.

The previous prime is 21606491. The next prime is 21606509. The reversal of 21606506 is 60560612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 19280881 + 2325625 = 4391^2 + 1525^2 .

It is a super-2 number, since 2×21606506² = 933682203056072, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21606509) 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 as a sum of consecutive naturals, namely, 5401625 + ... + 5401628.

Almost surely, 2^21606506 is an apocalyptic number.

21606506 is a deficient number, since it is larger than the sum of its proper divisors (10803256).

21606506 is a wasteful number, since it uses less digits than its factorization.

21606506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10803255.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 21606506 is about 4648.2798969081. The cubic root of 21606506 is about 278.5232884848.

The spelling of 21606506 in words is "twenty-one million, six hundred six thousand, five hundred six".