'How to add sequentials in a numbar using formula?

I need a Formula to use in my table, that will get me the following result

Please check this image

In B2 for example it is 1+2+3+4+5 In B3 As Another example it is 1+2+3+4+5+6 etc... thank you

Solution 1:^[1]

Try

Formula used in cell B2

=SUMPRODUCT(ROW(INDIRECT("1:"&$A2)))

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Solution	Source
Solution 1	Mayukh Bhattacharya