  Within the Bose-Einstein statistics it is shown that the blackbody radiation
contains coalescent photons along with single photons. Coalescent photons were
first observed in the famous Hong-Ou-Mandel experiment of 1987. For the sake of
convenience, $N$ coalescent photons are referred to as the $N$-photon cluster.
In this work, statistics of photon clusters and probability that a photon
cluster contains $N$ photons are found versus radiation frequency and
temperature. Spectra of photon-cluster radiation are calculated as functions of
blackbody temperature for different cluster ranks. Derivation of the Planck's
radiation law is discussed in view of the existence of photon clusters in
blackbody radiation.
