[Tex/LaTex] suppress indentation only after equation in LaTeX

Question

I am trying to make my LaTeX document only have indentation after equations. Other cases, including any lines of a paragraph block, no indentation.

This is a paragraph block that has many lines and I don't want indentation of any lines.

equations 1 here

Only the first line after equation need indentation. If this block has many lines, no indentation after first line.

Thanks for your help!

Edited:

Sorry I am new to this site. Here is the example I created. Hope that I addressed my problem clearly. Sorry for any inconvenience.

\documentclass[12pt]{article}

\setlength\parskip{12pt}

\begin{document}

I need help on this problem: indentation only after equation. For example, this is a paragraph not directly following an equation. Then it has no indentation to any of its lines.
\begin{equation}
  a = b+c
\end{equation}
This sentence directly follows an equation. Indentation is needed for the first line, only. 
\begin{equation}
  a = b*c
\end{equation}

This sentence starts a new paragraph, though directly follow an equation but no indentation for first line. Thanks.

Then I start a new paragraph. This paragraph, again, doesn't directly follow an equation. No indentation need.
I read an answer talking about blank line after equation. I understand this case. If I suppress a blank line after equation, it could give me indentation after equation. But it also gives me indentation of first line of every paragraph, which is not I wish to do. 

I have a silly solution that just add indent command to every sentence I want it indented. My question is could I have a worldwide solution? Thanks very much.


\end{document}

Answer 1

This is very strange request. But why not? You have set \parskip to 12pt, so the paragraphs are visible by this horizontal space. You can put the following three lines to your preamble:

\parindent=0pt
\everydisplay={\aftergroup\specindent}
\def\specindent{\global\hangindent=2em \global\hangafter=-1 \global\prevgraf=0 }