21681406 has 4 divisors (see below), whose sum is σ = 32522112. Its totient is φ = 10840702.

The previous prime is 21681389. The next prime is 21681421. The reversal of 21681406 is 60418612.

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

It is a super-2 number, since 2×21681406² = 940166732273672, which contains 22 as substring.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5420350 + ... + 5420353.

It is an arithmetic number, because the mean of its divisors is an integer number (8130528).

Almost surely, 2^21681406 is an apocalyptic number.

21681406 is a deficient number, since it is larger than the sum of its proper divisors (10840706).

21681406 is a wasteful number, since it uses less digits than its factorization.

21681406 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10840705.

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21681406 is about 4656.3296704593. The cubic root of 21681406 is about 278.8447554687.

The spelling of 21681406 in words is "twenty-one million, six hundred eighty-one thousand, four hundred six".