Maybe Tricky Dick was even tricker than we thought.
The 25th Amendment to the Constitution includes all the provisions covering resignation of a President. It specifies that such a resignation occurs
...whenever the President transmits to the president pro tempore of the Senate and the Speaker of the House of Representatives his written declaration that he is unable to discharge the powers and duties of his office.Nixon never did this!
Nixon submitted his resignation according to the procedures proscribed by an old law, a law that was superceded by the 25th amendment. Acting under the provisions of this old law, Nixon (apparently unaware that the law had been obsoleted by the recently-adopted constitutional amendment) submitted his resignation to the secretary of state, Henry Kissinger.
So Nixon's resignation was technically invalid, and though nobody realized it, Richard Nixon served two full terms!
Obviously, some facts can be accepted by empirical evidence, though, and Nixon's resignation would seem to be one of them. To make apparent fact jibe with law, the provisions of the 25th amendment could at least be said to have been met by saying that Nixon transmitted his resignation to the congressional leaders (as required), using Kissinger as his agent of transmission. Obviously, the persons to whom the Constitution requires the document to be transmitted did indeed eventually receive it or at least saw a copy of it in the public media (in which case Kissinger shared his duties as transmission agent with Walter Cronkite et al.). If the amendment called for the President to personally transmit the resignation to the speaker and the president pro tem, then I think we would have a more compelling case that Nixon served until 1977.
However, just a look at the letter of resignation shows that Nixon seemingly intended to transmit it only to the single named addressee -- the Secretary of State alone.
Short answer: probably. Despite the interesting facts above, it's pretty apparent from the sheer fact that he exercised the presidential powers without objection that Gerald Ford was the President of the United States.
Okay, you got me. It's not a frequently asked question. In fact, I've never been asked this question at all. I just like the answer.