21736 has 32 divisors (see below), whose sum is σ = 50400. Its totient is φ = 8640.

The previous prime is 21727. The next prime is 21737. The reversal of 21736 is 63712.

21736 = T₁₃ + T₁₄ + ... + T₅₀.

21736 is a nontrivial binomial coefficient, being equal to C(209, 2).

It is a Harshad number since it is a multiple of its sum of digits (19).

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (21737) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1135 + ... + 1153.

It is an arithmetic number, because the mean of its divisors is an integer number (1575).

2²¹⁷³⁶ is an apocalyptic number.

21736 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

21736 is the 208-th triangular number.

21736 is the 70-th centered nonagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21736, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25200).

21736 is an abundant number, since it is smaller than the sum of its proper divisors (28664).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21736 is a wasteful number, since it uses less digits than its factorization.

21736 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49 (or 45 counting only the distinct ones).

The product of its digits is 252, while the sum is 19.

The square root of 21736 is about 147.4313399519. The cubic root of 21736 is about 27.9078603941.

It can be divided in two parts, 217 and 36, that added together give a triangular number (253 = T₂₂).

The spelling of 21736 in words is "twenty-one thousand, seven hundred thirty-six".