#PHP, 45 bytes

<?php print number_format(pow(10,66))."a"; ?>

output:

1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a

<?php              //PHP start tag
print              //Prints what's ahead
number_format(arg) //format what's inside the parentheses as a number, with separators. (Used as escape function for having scientific notation result 
pow(base,exp)      //Gets the value of the `base` raised to the power of `exp`
.                  //Concatenation operator
"a"                //String of "a"
?>                 //End tag for PHP

PHP, 45 bytes

<?php print number_format(pow(10,66))."a"; ?>

output:

1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a

<?php              //PHP start tag
print              //Prints what's ahead
number_format(arg) //format what's inside the parentheses as a number, with separators. (Used as escape function for having scientific notation result 
pow(base,exp)      //Gets the value of the `base` raised to the power of `exp`
.                  //Concatenation operator
"a"                //String of "a"
?>                 //End tag for PHP

#PHP, 45 bytes

<?php print number_format(pow(10,66))."a"; ?>

output:

1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a

<?php
PHP start tag

print
Prints what's ahead

number_format(arg)
format what's inside the parentheses as a number, with separators. (Used as escape function for having scientific notation result

pow(base,exp)
Gets the value of the base raised to the power of exp

.
Concatenation operator

"a"
String that is equal to "a", without quotes. (Grrr.... the final touch of the code to get the output twice as the code's length :) )

?>
End tag for PHP

#PHP, 45 bytes

<?php print number_format(pow(10,66))."a"; ?>

output:

1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a

<?php              //PHP start tag
print              //Prints what's ahead
number_format(arg) //format what's inside the parentheses as a number, with separators. (Used as escape function for having scientific notation result 
pow(base,exp)      //Gets the value of the `base` raised to the power of `exp`
.                  //Concatenation operator
"a"                //String of "a"
?>                 //End tag for PHP

PHP, 45 bytes

code:
<?php print number_format(pow(10,66))."a"; ?>                                                                      45b

output: 1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a                                                                                                                                                      90b

#PHP, 45 bytes

<?php print number_format(pow(10,66))."a"; ?>

output:

1,000,000,000,000,000,132,394,543,446,603,018,655,781,305,157,705,474,440,625,207,115,776a

<?php
PHP start tag

print
Prints what's ahead

number_format(arg)
format what's inside the parentheses as a number, with separators. (Used as escape function for having scientific notation result

pow(base,exp)
Gets the value of the base raised to the power of exp

.
Concatenation operator

"a"
String that is equal to "a", without quotes. (Grrr.... the final touch of the code to get the output twice as the code's length :) )

?>
End tag for PHP