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- #!/usr/bin/ruby
- # Search for numbers k such that lcm({p-1}) and lcm({p+1}) are both small, where p are prime factor of k.
- # See also:
- # https://oeis.org/A334151
- var min = Inf
- for k in (1..1e7) {
- k.is_odd || next
- k.is_composite || next
- k.is_squarefree || next
- var a = k.factor.lcm{.dec}
- var b = k.factor.lcm{.inc}
- var r = ((a+b) / k)
- if (r < min) {
- min = r
- print(k, ", ")
- }
- }
- __END__
- 1, 3, 7, 15, 19, 31, 49, 99, 127, 241, 449, 511, 577, 703, 769, 799, 1249, 2177, 2889, 3401, 3725, 4351, 4751, 4801, 6049, 8191, 19601, 21295, 51841, 95831, 143749, 456191, 721279, 1062881, 1431431, 1623601, 1885521, 2101249, 3543121, 6215749,
- 1, 4, 8, 16, 27, 32, 64, 128, 243, 256, 512, 1024, 2048, 4096, 6561, 8192, 16384, 32768, 59049, 65536, 131072, 262144, 524288, 1048576,
- 1, 9, 25, 27, 75, 81, 225, 243, 625, 729, 2025, 2187, 6075, 6561, 15625, 19683, 50421, 59049, 151263, 177147, 390625, 531441, 1361367, 1594323, 4084101,
- 1, 10, 21, 30, 66, 110, 165, 210, 330, 651, 966, 1155, 1785, 1870, 2046, 2255, 2310, 3570, 4290, 4510, 4774, 5610, 6765, 7161, 10230, 11935, 13530, 14322, 23870, 35178, 35805, 58630, 71610, 175890, 410410, 615615,
- 15, 21, 55, 85, 105, 165, 399, 651, 1155, 1785, 2145, 2255, 2387, 2805, 5115, 6765, 7161, 11935, 17589, 29315, 35805, 87945, 205205, 498355, 508431, 608685, 615615, 1495065, 2378145, 2542155, 3488485, 3816813, 5775495, 6361355,
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