I came across this on http://sanskritdictionary.com/:
kubera kuberaḥ, yakṣarāṭ, yakṣendraḥ, yakṣeśvaraḥ, tryambakasakhā, guhyakeśvaraḥ, manuṣyadharmā, dhanadaḥ, dhanādhipaḥ, kinnareśaḥ, vaiśravaṇaḥ, paulastyaḥ, naravāhanaḥ, ekapiṅgaḥ, aiḍaviḍaḥ, śrīdaḥ, puṇyajaneśvaraḥ
yakṣānāṃ rājā yaḥ indrasya kośādhyakṣaḥ asti।
kuberaḥ rāvaṇasya bhrātā āsīt।
Is Indra grammatically irregular, so the "n," does not transform like normal? If so it would make his names easier to pronounce.
I also asked this here: https://hinduism.stackexchange.com/questions/43148/is-indra-grammatically-irregular
Edit: Text of screenshot by Severus Snape