# Maths: Sequence

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What is the nth term of the sequence:

1 4 10 20 35

I'm aware the differences follow the triangle number secuence, but what do I do now?

1 4 10 20 35

I'm aware the differences follow the triangle number secuence, but what do I do now?

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#2

I don't know much about the maths of triangle numbers, but I'd have a guess that n is the power of something.

Hmm... Well it's now obvious triangle numbers are just the addition of numbers, like a factoral where instead of multiplying you just add numbers.

I'll wait and see what other people have got.

Hmm... Well it's now obvious triangle numbers are just the addition of numbers, like a factoral where instead of multiplying you just add numbers.

I'll wait and see what other people have got.

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(Original post by

I don't know much about the maths of triangle numbers, but I'd have a guess that n is the power of something.

**mik1a**)I don't know much about the maths of triangle numbers, but I'd have a guess that n is the power of something.

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#4

(Original post by

What is the nth term of the sequence:

1 4 10 20 35

I'm aware the differences follow the triangle number secuence, but what do I do now?

**ZJuwelH**)What is the nth term of the sequence:

1 4 10 20 35

I'm aware the differences follow the triangle number secuence, but what do I do now?

*n*th term is n(n+1)(n+2)/6.

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(Original post by

Those are tetrahedral numbers. The

**Squishy**)Those are tetrahedral numbers. The

*n*th term is n(n+1)(n+2)/6.
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#7

(Original post by

Oh I see, like pyramid numbers.

**ZJuwelH**)Oh I see, like pyramid numbers.

SUM{r=1 -> n} r(r+1)/2

You can use the fact that

SUM{r=1 -> n} r = n(n+1)/2

SUM{r=1 -> n} r^2 = n(n+1)(2n+1)/6

to work out the formula that Squishy quoted.

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#8

(Original post by

Just a note of admiration for your signiture.

Very good indeed.

**samdavyson**)Just a note of admiration for your signiture.

Very good indeed.

(Original post by

Oh I see, like pyramid numbers.

**ZJuwelH**)Oh I see, like pyramid numbers.

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#9

(Original post by

Because the differences are the triange numbers, the nth term is the sum of the triangle numbers up to n. That is,

SUM{r=1 -> n} r(r+1)/2

You can use the fact that

SUM{r=1 -> n} r = n(n+1)/2

SUM{r=1 -> n} r^2 = n(n+1)(2n+1)/6

to work out the formula that Squishy quoted.

**mikesgt2**)Because the differences are the triange numbers, the nth term is the sum of the triangle numbers up to n. That is,

SUM{r=1 -> n} r(r+1)/2

You can use the fact that

SUM{r=1 -> n} r = n(n+1)/2

SUM{r=1 -> n} r^2 = n(n+1)(2n+1)/6

to work out the formula that Squishy quoted.

hello can u help me with maths its all about number grid i need the introduction if u can help me with plz

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#10

**ZJuwelH**)

What is the nth term of the sequence:

1 4 10 20 35

I'm aware the differences follow the triangle number secuence, but what do I do now?

0

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