<Tr> <Th> Base 36 </Th> <Td> </Td> </Tr> <P> 21 (twenty - one) is the natural number following 20 and preceding 22 . </P> <P> 21 is: </P> <Ul> <Li> a Blum integer, since it is a semiprime with both its prime factors being Gaussian primes . </Li> <Li> a Fibonacci number . </Li> <Li> a Harshad number . </Li> <Li> a Motzkin number . </Li> <Li> a triangular number . </Li> <Li> an octagonal number . </Li> <Li> a composite number, its proper divisors being 1, 3 and 7 . </Li> <Li> the sum of the first six natural numbers (1 + 2 + 3 + 4 + 5 + 6 = 21), making it a triangular number . </Li> <Li> the sum of the sum of the divisors of the first 5 positive integers . </Li> <Li> the smallest non-trivial example of a Fibonacci number whose digits are Fibonacci numbers and whose digit sum is also a Fibonacci number . </Li> <Li> a repdigit in base 4 (111). </Li> <Li> the smallest natural number that is not close to a power of 2, 2, where the range of closeness is ± n . </Li> <Li> the smallest number of differently sized squares needed to square the square . </Li> <Li> the largest n with this property: for any positive integers a, b such that a + b = n, at least one of a b (\ displaystyle (\ tfrac (a) (b))) and b a (\ displaystyle (\ tfrac (b) (a))) is a terminating decimal . See a brief proof below . </Li> </Ul>

What does number 21 means in the bible