A033198 - OEIS

A033198

Discriminants of real quadratic number fields.

8, 12, 5, 24, 28, 40, 44, 13, 56, 60, 17, 76, 21, 88, 92, 104, 29, 120, 124, 33, 136, 140, 37, 152, 156, 41, 168, 172, 184, 188, 204, 53, 220, 57, 232, 236, 61, 248, 65, 264, 268, 69, 280, 284, 73, 296, 77, 312, 316, 328, 332, 85, 344, 348, 89, 364, 93, 376, 380, 97

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OFFSET

1,1

REFERENCES

David A. Cox, "Primes of the Form x^2 + n y^2", Wiley, 1989, p. 103.

LINKS

Table of n, a(n) for n=1..60.

FORMULA

For squarefree n >= 2, list n if n=1 mod 4 else 4n.

MAPLE

with(numtheory): a:= proc(n) if issqrfree(n) then RETURN(piecewise(n mod 4=1, n, 4*n)) else RETURN(NULL) fi: end: seq(a(n), n=2..150); # C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 03 2005

MATHEMATICA

Reap[For[n = 2, n <= 100, n++, If[SquareFreeQ[n], Sow[If[Mod[n, 4] == 1, n, 4 n]]]]][[2, 1]] (* Jean-François Alcover, Mar 22 2023 *)

CROSSREFS

Cf. A144338.

Sequence in context: A004473 A114404 A173457 * A072900 A203836 A220665

Adjacent sequences: A033195 A033196 A033197 * A033199 A033200 A033201

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

EXTENSIONS

More terms from C. Ronaldo (aga_new_ac(AT)hotmail.com), Jan 03 2005

STATUS

approved