[Blindmath] Nemeth symbol question

[Sarah Jevnikar]

Hi all,
I came across a strange symbol I've never seen before. I'll transcribe the
whole line of math for context.

Capital f, followed by dots 5-6 (I assume a subscript), then a 0, then the
strange symbol: dots 2-4-6, followed by a capital t

In some cases, the t has been replaced with actual numbers. What does the
2-4-6 symbol mean? Anyone know where I can find a directory of non-standard
Nemeth symbols?

Thank you kindly,
Sarah Jevnikar