  The existence of the tiny neutrino mass and the flavor mixing can be
naturally explained by type-I Seesaw model which is probably the simplest
extension of the Standard Model (SM) using Majorana type SM gauge singlet heavy
Right Handed Neutrinos (RHNs). If the RHNs are around the Electroweak(EW)-scale
having sizable mixings with the SM light neutrinos, they can be produced at the
high energy colliders such as Large Hadron Collider (LHC) and future $100$ TeV
proton-proton (pp) collider through the characteristic signatures with same
sign di-lepton introducing lepton number violations(LNV). On the other hand
Seesaw models, namely inverse Seesaw, with small LNV parameter can accommodate
EW-scale pseudo-Dirac neutrinos with sizable mixings with SM light neutrinos
while satisfying the neutrino oscillation data. Due to the smallness of the LNV
parameter of such models, the `smoking-gun' signature of same-sign di-lepton is
suppressed where as the RHNs in the model will manifest at the LHC and future
$100$ TeV pp collider dominantly through the Lepton number conserving (LNC)
trilepton final state with Missing Transverse Energy (MET). Studying various
production channels of such RHNs we give an updated upper bound on the mixing
parameters of the light-heavy neutrinos at the 13 TeV LHC and future 100 TeV pp
collider.
