King goes to Havana

Over the years, 18 U.S. presidents have gone without a vice president at some point during their administration. I wonder if they noticed?

For the most part the vacancies were the result of there being no mechanism to replace the VP if he died, resigned or was promoted. The 25th Amendment, which deals with succession, changed that in 1967.

William Rufus DeVane King was elected Vice President on the Franklin Pierce ticket in 1852. He was ill with tuberculosis at the time. His doctors suggested that King go to Cuba for relief and he ended up taking the oath of office in Havana on March 24, 1853. From the New York Times of April 5, 1853:
  On the 24th inst., at 12 o’clock, the ceremony of administration of the oath to Mr. King as Vice-President of the United States, took place at the estate of Ariadne, by Wm. L. Sharkey, Consul of the United States at the Havana, assisted by Hon. George W. Jones, M.H.R. from Tennessee, and several American citizens who went down from Havana for the purpose of being present. The party were entertained by Mr. Chautrand, the proprietor, with generous hospitality, and every facility given for the appropriate performance of the duty.
  The gentlemen present, twelve or fifteen, represent Mr. King to be in an exceedingly delicate state of health—very feeble—and that he has not improved under the sugarhouse treatment advised for him by his physicians in the United States, — they also state his determination very soon, to Alabama, and it is supposed he will intermit, for the present, his sugarhouse exposure, and let the climate have a chance to give him strength, if it is not too late for that.
It was too late for that. He came back to Alabama and died two days later, on April 19, 1853. The sugar-house cure entailed drinking hot cane juice and also inhaling the vapors while the cane is being processed.