21006061 has 6 divisors (see below), whose sum is σ = 21959630. Its totient is φ = 20092248.

The previous prime is 21006053. The next prime is 21006071. The reversal of 21006061 is 16060012.

It can be written as a sum of positive squares in only one way, i.e., 20529961 + 476100 = 4531^2 + 690^2 .

It is not a de Polignac number, because 21006061 - 2³ = 21006053 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006071) 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 5 ways as a sum of consecutive naturals, for example, 19326 + ... + 20383.

Almost surely, 2^21006061 is an apocalyptic number.

It is an amenable number.

21006061 is a deficient number, since it is larger than the sum of its proper divisors (953569).

21006061 is an equidigital number, since it uses as much as digits as its factorization.

21006061 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39755 (or 39732 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21006061 is about 4583.2369565625. The cubic root of 21006061 is about 275.9189576872.

Adding to 21006061 its reverse (16060012), we get a palindrome (37066073).

The spelling of 21006061 in words is "twenty-one million, six thousand, sixty-one".