21612681 has 6 divisors (see below), whose sum is σ = 31218330. Its totient is φ = 14408448.

The previous prime is 21612677. The next prime is 21612691. The reversal of 21612681 is 18621612.

It can be written as a sum of positive squares in only one way, i.e., 13995081 + 7617600 = 3741^2 + 2760^2 .

It is not a de Polignac number, because 21612681 - 2² = 21612677 is a prime.

It is a super-2 number, since 2×21612681² = 934215960015522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21612601) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1200696 + ... + 1200713.

It is an arithmetic number, because the mean of its divisors is an integer number (5203055).

Almost surely, 2^21612681 is an apocalyptic number.

It is an amenable number.

21612681 is a deficient number, since it is larger than the sum of its proper divisors (9605649).

21612681 is a wasteful number, since it uses less digits than its factorization.

21612681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2401415 (or 2401412 counting only the distinct ones).

The product of its digits is 1152, while the sum is 27.

The square root of 21612681 is about 4648.9440736580. The cubic root of 21612681 is about 278.5498193438.

The spelling of 21612681 in words is "twenty-one million, six hundred twelve thousand, six hundred eighty-one".