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 A211259 Number of (n+1)X(n+1) -6..6 symmetric matrices with every 2X2 subblock having sum zero and one, three or four distinct values 1
 65, 335, 1703, 8645, 43643, 219333, 1097247, 5465297, 27114351, 134027929, 660336579, 3243840829, 15893481911, 77692754369, 379020868055, 1845782118641, 8974924575259, 43581782793301, 211388981838455, 1024316233634281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Symmetry and 2X2 block sums zero implies that the diagonal x(i,i) are equal modulo 2 and x(i,j)=(x(i,i)+x(j,j))/2*(-1)^(i-j) LINKS R. H. Hardin, Table of n, a(n) for n = 1..210 FORMULA Empirical: a(n) = 28*a(n-1) -155*a(n-2) -2658*a(n-3) +32061*a(n-4) +66366*a(n-5) -2314922*a(n-6) +3159336*a(n-7) +97801748*a(n-8) -317172988*a(n-9) -2797365748*a(n-10) +13347627288*a(n-11) +57922813108*a(n-12) -369288318800*a(n-13) -900259137962*a(n-14) +7525220569156*a(n-15) +10736644664141*a(n-16) -118794611594160*a(n-17) -100177501866905*a(n-18) +1492188101583602*a(n-19) +756635414359131*a(n-20) -15127411602979766*a(n-21) -4996517564711412*a(n-22) +124488915629652484*a(n-23) +32496342097994312*a(n-24) -830961220175609104*a(n-25) -217952927487180360*a(n-26) +4471006873093739800*a(n-27) +1356224545195754860*a(n-28) -19189501086495681880*a(n-29) -6829521421681422792*a(n-30) +64885315804531962064*a(n-31) +25455961312177735008*a(n-32) -171074565270467560384*a(n-33) -66023270051350386176*a(n-34) +350852776730555653120*a(n-35) +111115747477690885952*a(n-36) -562968030704836048256*a(n-37) -102780461262027908992*a(n-38) +705293155294335987968*a(n-39) -1905443632362091008*a(n-40) -673839571496082251776*a(n-41) +149968516817181865984*a(n-42) +463807639149162463232*a(n-43) -222954648389494145024*a(n-44) -202119207628642238464*a(n-45) +174410817888004440064*a(n-46) +32943327636122697728*a(n-47) -77835693049096830976*a(n-48) +15691242889927983104*a(n-49) +16793314088391802880*a(n-50) -9742537633650704384*a(n-51) -56226216776040448*a(n-52) +1727131956136640512*a(n-53) -597215426987950080*a(n-54) +331158386638848*a(n-55) +57745072535371776*a(n-56) -19695514744258560*a(n-57) +3305731101032448*a(n-58) -294085000691712*a(n-59) +11132555231232*a(n-60) EXAMPLE Some solutions for n=3 ..5.-4..1.-4....1.-2..3..0...-6..5.-3..5....3..0.-1.-2...-4..2..0..5 .-4..3..0..3...-2..3.-4..1....5.-4..2.-4....0.-3..4.-1....2..0.-2.-3 ..1..0.-3..0....3.-4..5.-2...-3..2..0..2...-1..4.-5..2....0.-2..4..1 .-4..3..0..3....0..1.-2.-1....5.-4..2.-4...-2.-1..2..1....5.-3..1.-6 CROSSREFS Sequence in context: A158693 A319617 A300162 * A069758 A116678 A218845 Adjacent sequences:  A211256 A211257 A211258 * A211260 A211261 A211262 KEYWORD nonn AUTHOR R. H. Hardin Apr 06 2012 STATUS approved

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Last modified December 9 17:18 EST 2019. Contains 329879 sequences. (Running on oeis4.)