A correlation coefficient has a range of -1 to 1. Any number outside of this range has been incorrectly calculated.
I note that is you meant to ask - Is r= -0.626 is a very strong correlation coefficient? then the answer No, this value is not a strong indicator that a linear relationship exists. Please see related link. The diagrams showing x-y graphs and the correlation coefficients is a good way to gain a "feel" of the coefficients and strength of relationships.
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