関連ワード:  first 10 triangular numbers    first 10 triangular numbers sum    first 10 triangular numbers formula    1st 10 triangular numbers    write first 10 triangular numbers    list first 10 triangular numbers    find the first 10 triangular numbers    first 10 triangular and square numbers    write the first 10 triangular numbers and find their sum    display the first 10 triangular numbers