Sequence Pattern Seq Odd Even Hard — Set 21

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{
    "title": "Hard Sequence Pattern #21",
    "sequenceType": "seq-odd-even",
    "displaySequence": [
        1,
        "_",
        5,
        7,
        "_",
        11,
        13,
        "_",
        17,
        19
    ],
    "fullSequence": [
        1,
        3,
        5,
        7,
        9,
        11,
        13,
        15,
        17,
        19
    ],
    "blankPositions": [
        1,
        4,
        7
    ],
    "answers": [
        3,
        9,
        15
    ],
    "rule": "Odd numbers in order",
    "question": "Find the 3 missing terms in the sequence: 1, _, 5, 7, _, 11, 13, _, 17, 19",
    "sequenceLength": 10,
    "hint": "Count by 2s starting at 1.",
    "_archetype": null,
    "_generatorId": null
}