Geometry optimizations and fragmentation energies of the series of hydrogen cyanide borane(1) oligomers (up to hixamers) and their dehydrogenated analogues are presented. Structural parameters are examined at different computational levels: MBPT(2) (second-order many-body perturbation theory), SDQ-MBPT(4) (fourth-order many-body perturbation theory limited to singly-, doubly-, and quadruply excited configurations), and DFT-B3LYP (density functional theory with Becke's three-parameter hybrid functional using the LeeYang-Parr correlation functional). These oligomers seem to be suitable input for the models of the polymer chain because of their periodic structure emerging from successive HCNBH or HCNB addition. The stability of the oligomers in terms of initial "cracking" of the weakest bond is fairly high, ranging from 97 to 443 kJ/mol for the HCNBH series and from 329 to 589 kJ/mol for the HCNB series.