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 A260854 Base-4 representation of a(n) is the concatenation of the base-4 representations of 1, 2, ..., n, n-1, ..., 1. 2
 0, 1, 25, 441, 27961, 7148857, 1830131001, 468514084153, 119939614479673, 30704541449950521, 7860362613477971257, 2012252829087011018041, 515136724246861226808633, 131875001407205856562222393, 33760000360244849399916500281, 8642560092222683848298425324857 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS The base 4 is listed in A260343, which means that a(4) = A260851(4) = 27961 is prime and therefore in A260852. See these sequences for more information. LINKS 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) = 25 = 16 + 2*4 + 1 = 121_4 is the concatenation of (1, 2, 1). a(4) = 27961 = 12310321_4 is the concatenation of (1, 2, 3, 10, 3, 2, 1), where the middle "10" is the base-4 representation of 4. PROG (PARI) a(n, b=4)=sum(i=1, #n=concat(vector(n*2-1, k, digits(min(k, n*2-k), b))), n[i]*b^(#n-i)) CROSSREFS Base-4 variant of A173426 (base 10) and A173427 (base 2). See A260853 - A260866 for variants in other bases b = 3, ..., 16. Sequence in context: A092430 A018207 A264382 * A001714 A016633 A001811 Adjacent sequences:  A260851 A260852 A260853 * A260855 A260856 A260857 KEYWORD nonn,base AUTHOR M. F. Hasler, Aug 01 2015 STATUS approved

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Last modified June 4 09:25 EDT 2020. Contains 334825 sequences. (Running on oeis4.)