There is a list with 19 elements ```a={0.500074`, 0.502676`, 0.510451`, 0.507502`, 0.52768`, 0.625164`,    0.935248`, 1.826161`, 3.845598`, 8.293859`, 18.014295`, 39.20736`,    85.3836`, 185.975252`, 405.095196`, 882.399269`, 1922.095421`,    4186.829292`, 9120.018288`}```

The elements in the list are written according to a certain rule that I don't know. I would like to expand this list in both directions like here ```anew={... a, b, c, 0.500074`, 0.502676`, 0.510451`, 0.507502`, 0.52768`, 0.625164`,    0.935248`, 1.826161`, 3.845598`, 8.293859`, 18.014295`, 39.20736`,    85.3836`, 185.975252`, 405.095196`, 882.399269`, 1922.095421`,    4186.829292`, 9120.018288`, d, e, f ...}``` where ```...a, b, c``` and ``` d, e, f...``` are elements which fit the general rule.

How to find this rule and write down additional elements (or just find the most suitable elements)?

All elements should be a positive

```
ClearAll["Global`*"]
a={0.500074`, 0.502676`, 0.510451`, 0.507502`, 0.52768`, 0.625164`,    0.935248`, 1.826161`, 3.845598`, 8.293859`, 18.014295`, 39.20736`,    85.3836`, 185.975252`, 405.095196`, 882.399269`, 1922.095421`,    4186.829292`, 9120.018288`};