21661012 has 12 divisors (see below), whose sum is σ = 38021620. Its totient is φ = 10797696.

The previous prime is 21661001. The next prime is 21661027. The reversal of 21661012 is 21016612.

It can be written as a sum of positive squares in 2 ways, for example, as 5692996 + 15968016 = 2386^2 + 3996^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6687 + ... + 9382.

Almost surely, 2^21661012 is an apocalyptic number.

It is an amenable number.

21661012 is a deficient number, since it is larger than the sum of its proper divisors (16360608).

21661012 is a wasteful number, since it uses less digits than its factorization.

21661012 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16410 (or 16408 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 19.

The square root of 21661012 is about 4654.1392329839. The cubic root of 21661012 is about 278.7572989033.

Adding to 21661012 its reverse (21016612), we get a palindrome (42677624).

The spelling of 21661012 in words is "twenty-one million, six hundred sixty-one thousand, twelve".