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A319019 First differences of A319018. 9
0, 1, 8, 8, 40, 8, 56, 24, 120, 8, 56, 48, 240, 40, 208, 56, 280, 8, 56, 48, 240, 64, 384, 120, 568, 56, 264, 144, 688, 112, 560, 136, 648, 8, 56, 48, 240, 64, 384, 136, 648, 72, 400, 232, 1128, 200, 1048, 240, 1216, 48, 216, 160, 768, 200, 1176, 352, 1664 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Number of cells added at n-th stage to the structure of A319018.

See A319018 for further illustrations.

LINKS

M. F. Hasler, Table of n, a(n) for n = 0..16384 (first 2050 terms from Rémy Sigrist)

Nathan Epstein, Gfycat animation of sequence.

M. F. Hasler, Interactive illustration of A319018 and A319019.

N. J. A. Sloane, Hand-drawn sketch showing terms through about the eighth shell, but using offset a(0)=1. Illustrates the octagonal "castle walls".

FORMULA

Apparently, a(2^k + 1) = 8 for any k >= 0.

a(n) = 8*A322050(n) for all n > 1, see there for more formulas. - M. F. Hasler, Dec 18 2018

PROG

(PARI) A319019_upto(N, S=[], K=[[t\5-2, t%5-2]|t<-digits(6888528048, 25)])={ vector(N, n, #N=if(n>1, S=setunion(S, N); N=vecsort(concat([[Vecsmall(Vec(n)+k)|k<-K]|n<-N])); S=setunion(Set(vecextract(N, select(i->N[i-1]==N[i], [2..#N]))), S); setminus(Set(N), S), [[0, 0]]))} \\ Increase stack size with allocatemem() for N > 86. - M. F. Hasler, Dec 27 2018

(PARI) A319019(n)=sum(i=2, n, A322050(i))*8+(n>0) \\ M. F. Hasler, Dec 28 2018

CROSSREFS

Cf. A319018.

For further analysis see A322048, A322049, A322050.

Sequence in context: A183400 A111218 A188275 * A278846 A240037 A241867

Adjacent sequences:  A319016 A319017 A319018 * A319020 A319021 A319022

KEYWORD

nonn

AUTHOR

Rémy Sigrist, Sep 09 2018

STATUS

approved

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Last modified July 20 15:59 EDT 2019. Contains 325185 sequences. (Running on oeis4.)