21686951 has 24 divisors (see below), whose sum is σ = 27214992. Its totient is φ = 17107200.

The previous prime is 21686947. The next prime is 21686957. The reversal of 21686951 is 15968612.

It is not a de Polignac number, because 21686951 - 2² = 21686947 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21686957) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 26336 + ... + 27146.

It is an arithmetic number, because the mean of its divisors is an integer number (1133958).

Almost surely, 2^21686951 is an apocalyptic number.

21686951 is a deficient number, since it is larger than the sum of its proper divisors (5528041).

21686951 is a wasteful number, since it uses less digits than its factorization.

21686951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 863 (or 852 counting only the distinct ones).

The product of its digits is 25920, while the sum is 38.

The square root of 21686951 is about 4656.9250584479. The cubic root of 21686951 is about 278.8685248739.

It can be divided in two parts, 2168 and 6951, that added together give a palindrome (9119).

The spelling of 21686951 in words is "twenty-one million, six hundred eighty-six thousand, nine hundred fifty-one".