Oh wait a minute, you said it's not on line 5a? What about 5b? If the taxable amount on 5b is the same as the gross distribution on 1099R box 1 then it doesn't show the amount on 5a.
See IRS 1040 Instructions page 26 middle column
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
It says........
If your pension or annuity is fully taxable, enter the total pension or annuity payments (from Form(s) 1099-R, box 1) on line 5b; don’t make an entry on line 5a.
