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 A245185 Triangle read by rows: T(n,k) = number of pseudo-square parallelogram (psp) polyominoes with semiperimeter n+1 and k columns. 3
 1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 1, 2, 5, 2, 1, 1, 3, 7, 7, 3, 1, 1, 3, 11, 15, 11, 3, 1, 1, 4, 15, 25, 25, 15, 4, 1, 1, 4, 20, 41, 52, 41, 20, 4, 1, 1, 5, 25, 62, 92, 92, 62, 25, 5, 1, 1, 5, 32, 89, 159, 179, 159, 89, 32, 5, 1, 1, 6, 38, 122, 249, 342, 342, 249, 122, 38, 6, 1 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,8 LINKS Andrew Howroyd, Table of n, a(n) for n = 1..300 Srecko Brlek, Andrea Frosini, Simone Rinaldi, Laurent Vuillon, Tilings by translation: enumeration by a rational language approach, The Electronic Journal of Combinatorics, vol. 13, (2006). See Table 2. EXAMPLE Triangle begins:   1;   1, 1;   1, 1,  1;   1, 2,  2,  1;   1, 2,  5,  2,  1;   1, 3,  7,  7,  3,  1;   1, 3, 11, 15, 11,  3,  1;   1, 4, 15, 25, 25, 15,  4, 1;   1, 4, 20, 41, 52, 41, 20, 4, 1;   ... PROG (PARI) IsPos(v)={for(i=1, #v, if(v[i]<=0, return(0))); 1} E(b)={my(v=vector(hammingweight(b)-1), h=0, k=0); if(bittest(b, 0), b>>=1); while(k<#v, if(bittest(b, 0), k++; v[k]=h, h++); b>>=1); v} Row(n)={my(v=vector(n)); forstep(b=2^n, 2*2^n, 2, my(r=E(b), d=b); for(k=1, n, d=bitor(d>>1, bitand(d, 1)<

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Last modified September 21 05:55 EDT 2020. Contains 337267 sequences. (Running on oeis4.)