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centered octagonal n.  and  interprime n.

First numbers that belong to both sets:

9, 81, 225, 441, 625, 1089, 1681, 2601, 13689, 16641, 25281, 27225, 38025, 45369, 56169, 74529, 87025, 91809, 95481, 106929, 149769, 154449, 184041, 194481, 199809, 216225, 223729, 263169, 314721, 321489, 328329, 370881, 393129, 540225, 651249, 804609, 822649, 931225, 950625, 970225, 1014049, 1071225, 1108809, 1121481, 1147041, 1234321, 1238769, 1306449, 1324801, 1343281, 1375929, 1520289, 1535121, 1610361, 1677025, 1713481, 1718721, 1782225, 1798281, 2047761, 2146225, 2411809, 2442969, 2449225, 2518569, 2588881, 2595321, 2614689, 2692881, 2778889, 2805625, 3017169, 3059001, 3243601, 3337929, 3381921, 3560769, 3636649, 3667225, 3721041, 3736489, 3775249, 3814209, 4272489, 4549689, 4609609, 4730625, 4774225, 4888521, 5058001, 5212089, 5433561, 5517801, 5527201, 5890329, 5978025, 6115729, 6405961, 6702921, 7241481, 7371225, 7403841, 7590025, 8003241, 8208225, 8381025, 8415801, 8439025, 8720209, 8732025, 9006001, 9030025, 9150625, 9272025, 9492561, 9566649, 10055241, 10413529, 11923209, 12595401, 12638025, 12752041, 12967201, 13111641, 13860729, 14070001, 14326225, 14493249, 15000129, 15046641, 15077689, 15657849, 16056049, 16589329, 16916769, 17015625, 17313921, 17464041, 17969121, 18088009, 18173169, 18533025, 18550249, 19000881, 20007729, 20025625, 20894041, 20912329, 21114025, 21279769, 21390625, 21427641, 21743569, 22724289, 22896225, 23126481, 23532201, 23648769, 23804641, 24750625, 25230529, 25310961, 25796241, 26286129, 26471025, 27029601, 27154521, 27300625, 28100601, 28355625, 29192409, 29343889, 29430625, 29844369, 29953729, 29975625, 30129121, 30525625, 30569841, 31348801, 32092225, 32433025, 33074001, 33350625, 33489369, 34257609, 34586161, 34869025, 35892081, 36180225, 36324729, 36978561, 37736449, 38229489, 38452401, 38900169, 39050001, 39075001, 39150049, 39627025, 39753025, 39879225, 39955041, 40030929, 40056241, 40208281, 40233649, 41177889, 41486481, 41744521, 42055225, 43837641, 44235801, 45360225, 45684081, 47430769, 47485881, 48316401, 48399849, 49154121, 49322529, 50083929, 50424201, 50993881, 51279921, 51394561, 51451929, 51796809, 51969681, 52056225, 52925625, 54952569, 57289761, 58018689, 60140025, 60233121, 60450625, 61355889, 62015625, 62078641, 62236321, 62805625, 64786401, 66438801, 66961489, 66994225, 67026969, 67223601, 67420521, 67453369, 67980025, 68906601, 68939809, 69505569, 69705801, 70274689, 71149225, 71318025, 71588521, 72607441, 72846225, 73324969, 75429225, 76685049, 77951241, 78163281, 78801129, 79227801, 79334649, 80299521, 81378441, 81558961, 81739681, 82174225, 82210489, 82391929, 82682649, 84217329, 88115769, 88454025, 88868329, 89397025, 89813529, 91565761, 91757241, 92563641, 94536729, 94653441, 95160025, 95238081, 96059601, 96412761, 96727225, 97357689, 97594641, 97831881, 98188281, 98545329.