K is called real quadratic if d > 0. K has class number 1 for the following values of d (sequence A003172 in the OEIS):
2*, 3, 5*, 6, 7, 11, 13*, 14, 17*, 19, 21, 22, 23, 29*, 31, 33, 37*, 38, 41*, 43, 46, 47, 53*, 57, 59, 61*, 62, 67, 69, 71, 73*, 77, 83, 86, 89*, 93, 94, 97*, ...
K has class number 1 exactly for the following negative values of d:
−1, −2, −3, −7, −11, −19, −43, −67, −163