By the time Modi is through with 6 months in office, he will have spent 29 to 30 days on foreign soil- which is a record. Dr Manmohan Singh, his predecessor too made quite a number of trips but comes second to Modi. Despite the numerous trips taken by Dr Singh, he could not manage staying away from the nation for continuous 12 days in a month.
Evidently pressures of dealing with a coalition government for decades resulted in Prime Ministers like Atal Behari and Narasimha Rao to stay put. Atal Bihari Vajpayee traveled little.
Leaders like V P Singh, Chandra Shekhar, H D Deve Gowda and I K Gujral can hardly be counted in the list as their governments lasted barely a year each, or they headed a minority government.
Former Prime Ministers like Nehru, Indira Gandhi, Rajiv Gandhi and Morarji Desai led a majority government in the Lower House, but back then there were not many multilateral summits - like BRICS, IBSA, East Asia Summit, etc. Most of these were formed in the 90ies.
Comparatively, Nehru's visit to Bhutan on horseback and on foot was one long and memorable trip in 1958. Indira Gandhi traveled to the Western nations before Bangladesh War in 1971. V P Singh and Vajpayee traveled for eight to ten days when they had to attend United Nations General Assembly in the US.