human: Given a node-centered hypergraph: <hypergraph>, where nodes represent papers and hyperedges represent sets of papers co-cited by a source paper.

Details of the hypergraph:
Center node: "pythagorean triples and cryptographic coding"
  Abstract: This paper summarizes basic properties of PPTs and shows that each PPT belongs to one of six different classes. Mapping an ordered sequence of PPTs into a corresponding sequence of these six classes makes it possible to use them in cryptography. We pose problems whose solution would facilitate such cryptographic application.

Connected through hyperedge HE-1 (induced by source paper "residue classes of the ppt sequence"):
  with members:
    - "random sequences from primitive pythagorean triples"

Connected through hyperedge HE-2 (induced by source paper "random sequences from primitive pythagorean triples"):
  with members:
    - "random sequences based on the divisor pairs function"
    - "goldbach circles and balloons and their cross correlation"
    - "new results on scrambling using the mesh array"
    - "on the mesh array for matrix multiplication"
    - "analysis of prime reciprocal sequences in base 10"

Connected through hyperedge HE-3 (induced by source paper "goldbach circles and balloons and their cross correlation"):
  with members:
    - "on randomness of goldbach sequences"
    - "goldbach ellipse sequences for cryptographic applications"
    - "goldbach triples and key distribution"
    - "analysis of prime reciprocal sequences in base 10"

Connected through hyperedge HE-4 (induced by source paper "goldbach triples and key distribution"):
  with members:
    - "on randomness of goldbach sequences"
    - "goldbach ellipse sequences for cryptographic applications"
    - "on the mesh array for matrix multiplication"
    - "analysis of prime reciprocal sequences in base 10"

Connected through hyperedge HE-5 (induced by source paper "random sequences based on the divisor pairs function"):
  with members:
    - "goldbach circles and balloons and their cross correlation"
    - "on the mesh array for matrix multiplication"

Connected through hyperedge HE-6 (induced by source paper "indexing properties of primitive pythagorean triples for cryptography applications"):
  with members:
    - "the cubic public key transformation"

Question: Please tell me which class the center node belongs to. The 40 classes are: cs.NA(Numerical Analysis), cs.MM(Multimedia), cs.LO(Logic in Computer Science), cs.CY(Computers and Society), cs.CR(Cryptography and Security), cs.DC(Distributed, Parallel, and Cluster Computing), cs.HC(Human-Computer Interaction), cs.CE(Computational Engineering, Finance, and Science), cs.NI(Networking and Internet Architecture), cs.CC(Computational Complexity), cs.AI(Artificial Intelligence), cs.MA(Multiagent Systems), cs.GL(General Literature), cs.NE(Neural and Evolutionary Computing), cs.SC(Symbolic Computation), cs.AR(Hardware Architecture), cs.CV(Computer Vision and Pattern Recognition), cs.GR(Graphics), cs.ET(Emerging Technologies), cs.SY(Systems and Control), cs.CG(Computational Geometry), cs.OH(Other Computer Science), cs.PL(Programming Languages), cs.SE(Software Engineering), cs.LG(Machine Learning), cs.SD(Sound), cs.SI(Social and Information Networks), cs.RO(Robotics), cs.IT(Information Theory), cs.PF(Performance), cs.CL(Computation and Language), cs.IR(Information Retrieval), cs.MS(Mathematical Software), cs.FL(Formal Languages and Automata Theory), cs.DS(Data Structures and Algorithms), cs.OS(Operating Systems), cs.GT(Computer Science and Game Theory), cs.DB(Databases), cs.DL(Digital Libraries), cs.DM(Discrete Mathematics). Directly output the class name.

gpt: cs.CR(Cryptography and Security)