This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A344079 #13 May 09 2021 10:48:07 %S A344079 12,16,20,72,88,92,104,128,136,164,172,184,188,192,236,243,244,256, %T A344079 260,264,272,276,284,292,296,316,332,336,340,342,344,348,364,372,376, %U A344079 388,392,396,400,416,420,440,456,468,484,488,496,504,536,548,560,576,596,600,608,612,620,637,640,644,652,664 %N A344079 Numbers m such that A060649(m) > 0 and that C(-A060649(m)) is not cyclic, where C(D) is the class group of the quadratic field with discriminant D. %C A344079 Assume that for all n, we have A060649(n) > 0 and either A344072(n) = 0 or A344072(n) > A060649(2n), then this sequence gives the indices where A060649 and A344073 differ. %C A344079 All terms must be nonsquarefree, since an abelian group of squarefree order must be cyclic. %e A344079 The smallest k == 3 (mod 4) such that Q(sqrt(-k)) has class number 12 is k = -231, but the class group of Q(sqrt(-231)) is isomorphic to C_2 X C_6, which is not cyclic, so 12 is a term. %e A344079 The smallest k == 3 (mod 4) such that Q(sqrt(-k)) has class number 20 is k = -455, but the class group of Q(sqrt(-455)) is isomorphic to C_2 X C_10, which is not cyclic, so 20 is a term. %e A344079 The smallest k == 3 (mod 4) such that Q(sqrt(-k)) has class number 637 is k = -149519, but the class group of Q(sqrt(-149519)) is isomorphic to C_7 X C_91, which is not cyclic, so 637 is a term. %o A344079 (PARI) isA344079(n) = my(d=3); while(!isfundamental(-d) || qfbclassno(-d)!=n, d+=4); #quadclassunit(-d)[2]>1 %Y A344079 Cf. A060649, A344073, A344072. %K A344079 nonn %O A344079 1,1 %A A344079 _Jianing Song_, May 08 2021