Declension table of ?ṛdhaṅmantra

Masculine	Singular	Dual	Plural
Nominative	ṛdhaṅmantraḥ	ṛdhaṅmantrau	ṛdhaṅmantrāḥ
Vocative	ṛdhaṅmantra	ṛdhaṅmantrau	ṛdhaṅmantrāḥ
Accusative	ṛdhaṅmantram	ṛdhaṅmantrau	ṛdhaṅmantrān
Instrumental	ṛdhaṅmantreṇa	ṛdhaṅmantrābhyām	ṛdhaṅmantraiḥ ṛdhaṅmantrebhiḥ
Dative	ṛdhaṅmantrāya	ṛdhaṅmantrābhyām	ṛdhaṅmantrebhyaḥ
Ablative	ṛdhaṅmantrāt	ṛdhaṅmantrābhyām	ṛdhaṅmantrebhyaḥ
Genitive	ṛdhaṅmantrasya	ṛdhaṅmantrayoḥ	ṛdhaṅmantrāṇām
Locative	ṛdhaṅmantre	ṛdhaṅmantrayoḥ	ṛdhaṅmantreṣu

Compound ṛdhaṅmantra -

Adverb -ṛdhaṅmantram -ṛdhaṅmantrāt