21019681 has 8 divisors (see below), whose sum is σ = 22227200. Its totient is φ = 19822320.

The previous prime is 21019657. The next prime is 21019699. The reversal of 21019681 is 18691012.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21019681 - 2¹⁵ = 20986913 is a prime.

It is a super-2 number, since 2×21019681² = 883653978683522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21019601) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1936 + ... + 6766.

It is an arithmetic number, because the mean of its divisors is an integer number (2778400).

Almost surely, 2^21019681 is an apocalyptic number.

It is an amenable number.

21019681 is a deficient number, since it is larger than the sum of its proper divisors (1207519).

21019681 is a wasteful number, since it uses less digits than its factorization.

21019681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5079.

The product of its (nonzero) digits is 864, while the sum is 28.

The square root of 21019681 is about 4584.7225652159. The cubic root of 21019681 is about 275.9785786427.

It can be divided in two parts, 210 and 19681, that added together give a palindrome (19891).

The spelling of 21019681 in words is "twenty-one million, nineteen thousand, six hundred eighty-one".