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The converse of the statement above is, however, not always true. For example, the digital root of 12, which is not a triangular number, is 3 and divisible by three. If x is a triangular number, a is an odd square, and b = a − 1 / 8 , then ax + b is also a triangular number.
The triangular number sequence is the representation of the numbers in the form of equilateral triangle arranged in a series or sequence. These numbers are in a sequence of 1, 3, 6, 10, 15, 21, 28, 36, 45, and so on.
The nth partial sum is given by a simple formula: = = (+). This equation was known to the Pythagoreans as early as the sixth century BCE. [5] Numbers of this form are called triangular numbers, because they can be arranged as an equilateral triangle.
A tetrahedral number, or triangular ... The formula for the n th tetrahedral number is represented by ... to figurate numbers. Te 12 = 364 is the total ...
Consequently, a square number is also triangular if and only if + is square, that is, there are numbers and such that =. This is an instance of the Pell equation x 2 − n y 2 = 1 {\displaystyle x^{2}-ny^{2}=1} with n = 8 {\displaystyle n=8} .
The first few pentagonal numbers are: 1, 5, 12, 22 ... where T n is the nth triangular number: ... Generalized pentagonal numbers are obtained from the formula given ...
Each centered triangular number has a remainder of 1 when divided by 3, and the quotient (if positive) is the previous regular triangular number. Each centered triangular number from 10 onwards is the sum of three consecutive regular triangular numbers. For n > 2, the sum of the first n centered triangular numbers is the magic constant for an n ...
The th doubly triangular number is given by the quartic formula [2] = (+) (+ +). The sums of row sums of Floyd's triangle give the doubly triangular numbers. Another way of expressing this fact is that the sum of all of the numbers in the first n {\displaystyle n} rows of Floyd's triangle is the n {\displaystyle n} th doubly triangular number.