A359149 - OEIS

A359149

Concatenate the binary strings for 1,2,...,n-1, n, n-1, ..., 2,1.

1, 1101, 11011101, 1101110011101, 1101110010110011101, 1101110010111010110011101, 1101110010111011111010110011101, 11011100101110111100011111010110011101, 1101110010111011110001001100011111010110011101, 110111001011101111000100110101001100011111010110011101

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OFFSET

1,2

COMMENTS

Binary analog of A173426 and A360504.

Converting these binary strings to base 10 gives A173427. E.g. 1101_2 = 13_10 gives A173427(3) = 13.

What is the first prime here if these strings are regarded as decimal numbers as they stand? a(5) = 1101110010110011101 = 3*37*53*187168113226247 is obviously not a prime.

LINKS

Table of n, a(n) for n=1..10.

Index entries for sequences related to Most Wanted Primes video

MAPLE

a:= n-> parse(cat(map(t-> convert(t, binary), [$1..n, n-i$i=1..n-1])[])):

seq(a(n), n=1..10); # Alois P. Heinz, Feb 18 2023

MATHEMATICA

a[n_] := FromDigits @ Flatten @ IntegerDigits[Join[Range[1, n], Range[n - 1, 1, -1]], 2]; Array[a, 10] (* Amiram Eldar, Feb 18 2023 *)

PROG

(Python)

from itertools import count, islice

def agen(): # generator of terms