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 A224666 Number of 4 X 4 0..n matrices with each 2 X 2 subblock idempotent. 1
 78, 108, 142, 180, 222, 268, 318, 372, 430, 492, 558, 628, 702, 780, 862, 948, 1038, 1132, 1230, 1332, 1438, 1548, 1662, 1780, 1902, 2028, 2158, 2292, 2430, 2572, 2718, 2868, 3022, 3180, 3342, 3508, 3678, 3852, 4030, 4212, 4398, 4588, 4782, 4980, 5182 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 2*n^2 + 24*n + 52. Conjectures from Colin Barker, Sep 02 2018: (Start) G.f.: 2*x*(39 - 63*x + 26*x^2) / (1 - x)^3. a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n>3. (End) EXAMPLE Some solutions for n=3: ..1..0..0..0....1..0..0..0....1..1..0..1....1..0..1..0....1..0..0..0 ..0..0..0..0....1..0..0..1....0..0..0..1....0..0..1..0....1..0..0..0 ..0..0..0..0....1..0..0..1....0..0..0..1....0..0..1..0....1..0..0..0 ..0..0..0..1....0..0..0..1....0..0..0..1....0..0..1..0....0..0..1..1 CROSSREFS Row 4 of A224665. Sequence in context: A025387 A025378 A157355 * A161596 A275218 A260364 Adjacent sequences: A224663 A224664 A224665 * A224667 A224668 A224669 KEYWORD nonn AUTHOR R. H. Hardin, Apr 14 2013 STATUS approved

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Last modified September 30 19:35 EDT 2023. Contains 365793 sequences. (Running on oeis4.)