21002661 has 12 divisors (see below), whose sum is σ = 30389580. Its totient is φ = 13977600.

The previous prime is 21002651. The next prime is 21002671. The reversal of 21002661 is 16620012.

It is a happy number.

21002661 is a `hidden beast` number, since 2 + 1 + 0 + 0 + 2 + 661 = 666.

It is an interprime number because it is at equal distance from previous prime (21002651) and next prime (21002671).

It can be written as a sum of positive squares in 2 ways, for example, as 13549761 + 7452900 = 3681^2 + 2730^2 .

It is not a de Polignac number, because 21002661 - 2⁵ = 21002629 is a prime.

It is a super-2 number, since 2×21002661² = 882223538161842, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002621) 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 11 ways as a sum of consecutive naturals, for example, 4645 + ... + 7973.

It is an arithmetic number, because the mean of its divisors is an integer number (2532465).

Almost surely, 2^21002661 is an apocalyptic number.

It is an amenable number.

21002661 is a deficient number, since it is larger than the sum of its proper divisors (9386919).

21002661 is a wasteful number, since it uses less digits than its factorization.

21002661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4036 (or 4033 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21002661 is about 4582.8660246619. The cubic root of 21002661 is about 275.9040703162.

Adding to 21002661 its reverse (16620012), we get a palindrome (37622673).

It can be divided in two parts, 2100 and 2661, that added together give a square (4761 = 69²).

The spelling of 21002661 in words is "twenty-one million, two thousand, six hundred sixty-one".