Historical clue formulations

• Symbol used in summation — 2026-05-22
• Letter between rho and tau — 2026-01-06
• Greek letter that refers to a lone wolf, in Gen-Z slang — 2025-10-10
• Summation symbol, in math — 2025-02-10
• Greek letter that represents summation — 2025-01-21
• Greek "S" — 2023-05-01
• It's at the end of "Oedipus" — 2023-03-25
• Symbol for stock volatility, in finance — 2021-08-28
• Letter after rho — 2021-03-15
• Letter before tau — 2020-02-10
• Summation symbol, in math — 2019-01-31
• Rho follower — 2018-12-26
• Arithmetic series symbol — 2018-03-15
• Letter before 7-Down — 2016-05-26
• Standard deviation symbol — 2015-06-14
• Rho-tau linkup — 2014-10-21
• Sum symbol — 2014-01-11
• Summation symbol in math — 2012-04-17
• Greek "S" — 2012-04-02
• Head of ancient Sparta? — 2012-01-22
• Summation signifier, in math — 2011-06-21
• Symbol in a Riemann sum — 2009-11-19
• Summation symbol — 2009-09-29
• Arithmetic series symbol — 2009-03-15
• Standard deviation symbol — 2006-11-04
• Calculus symbol — 2005-12-06
• Standard deviation symbol — 2004-02-15
• ___ Society (super-high I.Q. group) — 2002-08-18
• Science society ___ Xi — 2002-07-24
• Symbol of conductivity — 2001-09-30
• Standard deviation symbol — 2001-07-15
• Fraternity letter — 2000-12-02
• ___ Alpha Epsilon fraternity — 1999-06-15
• Greek S — 1999-03-23
• Greek letter — 1997-04-28