  We are using the LOw-Frequency ARray (LOFAR) to perform the LOFAR Tied-Array
All-Sky (LOTAAS) survey for pulsars and fast transients. Here we present the
astrometric and rotational parameters of 20 pulsars discovered as part of
LOTAAS. These pulsars have regularly been observed with LOFAR at 149 MHz and
the Lovell telescope at 1532 MHz, supplemented by some observations with the
Lovell telescope at 334 MHz and the Nancay Radio Telescope at 1484 MHz. Timing
models are calculated for the 20 pulsars, some of which are among the
slowest-spinning pulsars known. PSR J1236-0159 rotates with a period P ~ 3.6 s,
while 5 additional pulsars show P > 2 s. Also, the spin-down rates Pdot are, on
average, low, with PSR J0815+4611 showing Pdot ~ 4E-18. Some of the pulse
profiles, generically single-peaked, present complex shapes evolving with
frequency. Multi-frequency flux measurements show that these pulsars have
generically relatively steep spectra but exceptions are present, with values
ranging between ~ -4 and -1. Among the pulsar sample, a large fraction shows
large single-pulse variability, with 4 pulsars being undetectable more than 15%
of the time and one tentatively classified as a Rotating Radio Transient. Two
single-peaked pulsars show drifting sub-pulses.
