A355879 Class number of Q(sqrt((-1)^((p-1)/2)*p)), where p = prime(n).
1, 1, 1, 1, 1, 1, 1, 1, 3, 1, 3, 1, 1, 1, 5, 1, 3, 1, 1, 7, 1, 5, 3, 1, 1, 1, 5, 3, 1, 1, 5, 5, 1, 3, 1, 7, 1, 1, 11, 1, 5, 1, 13, 1, 1, 9, 3, 7, 5, 3, 1, 15, 1, 7, 3, 13, 1, 11, 1, 1, 3, 1, 3, 19, 1, 1, 3, 1, 5, 1, 1, 19, 9, 1, 3, 17, 1, 1, 5, 1, 9, 1, 21, 1, 15, 5, 1, 1, 1, 7
Offset: 1
Keywords
Examples
prime(9) = 23, Q(sqrt(-23)) has class number 3, so a(9) = 3. prime(15) = 47, Q(sqrt(-47)) has class number 5, so a(15) = 5. prime(20) = 71, Q(sqrt(-71)) has class number 7, so a(20) = 7. prime(50) = 229, Q(sqrt(229)) has class number 3, so a(50) = 3.
Links
Programs
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PARI
a(n) = if(n==1, 1, my(p=prime(n)); qfbclassno(if(p%4==1, p, -p)))
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