search.sf

#!/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,