The function is known to change sign infinitely often, but so far all calculated values are positive. In this paper we prove that the first sign change occurs well before exp(495.702833165).
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-2-5, author = {Jan B\"uthe}, title = {On the first sign change in Mertens' theorem}, journal = {Acta Arithmetica}, volume = {168}, year = {2015}, pages = {183-195}, zbl = {06497308}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-2-5} }
Jan Büthe. On the first sign change in Mertens' theorem. Acta Arithmetica, Tome 168 (2015) pp. 183-195. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-2-5/