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A027389
Write decimal digits for n, count endpoints (version 4).
4
0, 2, 2, 2, 4, 2, 1, 4, 0, 1, 2, 4, 4, 4, 6, 4, 3, 6, 2, 3, 2, 4, 4, 4, 6, 4, 3, 6, 2, 3, 2, 4, 4, 4, 6, 4, 3, 6, 2, 3, 4, 6, 6, 6, 8, 6, 5, 8, 4, 5, 2, 4, 4, 4, 6, 4, 3, 6, 2, 3, 1, 3, 3, 3, 5, 3, 2, 5, 1, 2, 4, 6, 6, 6, 8, 6, 5, 8, 4, 5, 0
OFFSET
0,2
COMMENTS
Number of endpoints: 0,8 - zero, 6,9 - one, 1,2,3,5 - two, 4,7 - four. - Michael B. Porter, Oct 28 2017
FORMULA
a(10*n + d) = a(n) + e where e is the number of endpoints of single digit d. - David A. Corneth, Oct 28 2017
EXAMPLE
The digit 1 has two endpoints, and the digit 8 has no endpoints, so a(18) = 2. - Michael B. Porter, Oct 28 2017
MATHEMATICA
Table[Total[IntegerDigits[n]/.{1->2, 3->2, 5->2, 6->1, 7->4, 8->0, 9->1}], {n, 0, 100}] (* Harvey P. Dale, May 08 2022 *)
PROG
(PARI) a(n)=vecsum(apply(d->[0, 2, 2, 2, 4, 2, 1, 4, 0, 1][d+1], digits(n))); \\ based on program for A027386 by Andrew Howroyd, Michael B. Porter, Oct 28 2017
KEYWORD
nonn,base
EXTENSIONS
a(6) corrected by Michael B. Porter, Oct 28 2017 (per Andrew Howroyd)
a(27) to a(80) by Michael B. Porter, Oct 28 2017
STATUS
approved