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A365159
a(n)=n for n<=3, and thereafter, a(n) is the number of locations 1..n-1 which cannot be reached starting from i=n-1, where jumps from location i to i +- a(i) are permitted (within 1..n-1). See example.
1
1, 2, 3, 2, 2, 3, 4, 4, 3, 6, 4, 6, 8, 5, 9, 10, 11, 12, 13, 13, 11, 11, 13, 13, 15, 15, 16, 17, 18, 19, 20, 20, 21, 22, 23, 24, 25, 26, 26, 18, 26, 29, 20, 23, 24, 25, 26, 27, 28, 29, 29, 28, 31, 29, 28, 29, 30, 31, 32, 33, 34, 34, 38, 27, 39, 40, 41, 42, 42
OFFSET
1,2
LINKS
EXAMPLE
a(9)=3 because there are 3 locations that cannot be reached starting from i=n-1=8, where a(8)=4. We start by finding the locations that can be reached (each line shows the next unvisited location(s) we can reach from the term(s) in the previous iteration):
1, 2, 3, 2, 2, 3, 4, 4
2<----------4
1, 2, 3, 2, 2, 3, 4, 4
2<----2---->3
1, 2, 3, 2, 2, 3, 4, 4
3<-------3
We visited 5 locations (i = 2, 3, 4, 6, and 8) and can visit no more:
1, 2, 3, 2, 2, 3, 4, 4
2 3 2 3 4
This leaves a total of 3 locations that could not be reached (i = 1, 5, and 7) from i=8, so a(9)=3.
CROSSREFS
Cf. A360746.
Sequence in context: A303540 A137266 A062948 * A358639 A358640 A096258
KEYWORD
nonn
AUTHOR
Neal Gersh Tolunsky, Aug 23 2023
STATUS
approved