וְסָפַרְתָּ֣ לְךָ֗ שֶׁ֚בַע שַׁבְּתֹ֣ת שָׁנִ֔ים שֶׁ֥בַע שָׁנִ֖ים שֶׁ֣בַע פְּעָמִ֑ים וְהָי֣וּ לְךָ֗ יְמֵי֙ שֶׁ֚בַע שַׁבְּתֹ֣ת הַשָּׁנִ֔ים תֵּ֥שַׁע וְאַרְבָּעִ֖ים שָׁנָֽה׃
And thou shalt number seven sabbaths of years unto thee, seven times seven years; and there shall be unto thee the days of seven sabbaths of years, even forty and nine years.
Read kabbalistic (mystical) interpretation of Leviticus 25:8: and classical mystical sources.