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A260853 Base-3 representation of a(n) is the concatenation of the base-3 representations of 1, 2, ..., n, n-1, ..., 1. 20
0, 1, 16, 439, 35350, 2864599, 232046890, 18795930559, 1522471570630, 369960528437035, 269701223137448146, 196612191672080116867, 143330287729139571972130, 104487779754548024866115515, 76171591441065652665051372946, 55529090160536864641400481743827 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

The base 3 is listed in A260343, which means that a(3) = A260851(3) = 439 = 121021_3 is prime and therefore in A260852. See these sequences for more information.

LINKS

Table of n, a(n) for n=0..15.

D. Broadhurst, Primes from concatenation: results and heuristics, NmbrThry List, August 1, 2015

EXAMPLE

a(0) = 0 is the result of the empty sum corresponding to 0 digits.

a(2) = 16 = 121_3 is the concatenation of (1, 2, 1).

a(3) = 439 = 121021_3 is the concatenation of (1, 2, 10, 2, 1), where the middle "10" is the base-3 representation of 3.

MATHEMATICA

Join[{0}, Table[FromDigits[Join[Flatten[IntegerDigits[Range[n], 3]], Flatten[ Reverse[ Most[ IntegerDigits[Range[n], 3]]]]], 3], {n, 20}]] (* Harvey P. Dale, Mar 11 2019 *)

PROG

(PARI) a(n, b=3)=sum(i=1, #n=concat(vector(n*2-1, k, digits(min(k, n*2-k), b))), n[i]*b^(#n-i))

CROSSREFS

Base-3 variant of A173426 (base 10) and A173427 (base 2). See A260854 - A260866 for variants in other bases b = 4, ..., 16.

Sequence in context: A223686 A000489 A075852 * A068792 A229583 A241077

Adjacent sequences:  A260850 A260851 A260852 * A260854 A260855 A260856

KEYWORD

nonn,base

AUTHOR

M. F. Hasler, Aug 01 2015

STATUS

approved

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Last modified June 20 23:12 EDT 2021. Contains 345310 sequences. (Running on oeis4.)