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 A173427 Decimal value a(n) of the binary number b(n) obtained by starting from 1, sequentially concatenating all binary numbers up to n and then sequentially concatenating all binary numbers from n-1 down to 1. 23
 1, 13, 221, 7069, 451997, 28931485, 1851651485, 237010810269, 60674754606493, 15532737233548701, 3976380732916495773, 1017953467644930815389, 260596087717395474544029, 66712598455657932715586973 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) = binary_to_decimal(concatenate(1,10,11,..., binary(n-2), binary(n-1), binary(n), binary(n-1), binary(n-2),..., 11, 10, 1)) EXAMPLE a(1)=binary_to_decimal(1)=1, a(2)=binary_to_decimal(1101)=13, a(3)=binary_to_decimal(11011101)=221, a(4)=binary_to_decimal(1101110011101)=7069 etc. PROG (PARI) a(n)=sum(i=1, #n=concat(vector(n*2-1, k, binary(min(k, n*2-k)))), n[i]<<(#n-i)) (PARI) A173427(n)={my(s=0, s1=0, t=0, b=0); for(k=1, n-1, s1+=k<>b&&b++; s=s<>b&&b++; (s<

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Last modified October 21 18:54 EDT 2019. Contains 328308 sequences. (Running on oeis4.)