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- #!/usr/bin/ruby
- # a(n) is the smallest k such that usigma(k) = A002110(n), or 0 if no such k exists.
- # https://oeis.org/A291356
- # Known terms:
- # 1, 0, 5, 18, 164, 1538, 20018, 408404, 7759748, 148728578, 0, 194482899488, 0, 286353189202064, 0, 491911826070793124, 32087786808310197824, 1809656800145141307344, 113734187984879487014048, 0, 0, 27153120399499349433747548978, 0
- for k in (1..30) {
- print(k.pn_primorial.inverse_usigma.first || 0, ", ")
- }
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