A027387 Write digits for n, count endpoints (version 2).

0, 2, 2, 2, 4, 2, 1, 2, 0, 1, 2, 4, 4, 4, 6, 4, 3, 4, 2, 3, 2, 4, 4, 4, 6, 4, 3, 4, 2, 3, 2, 4, 4, 4, 6, 4, 3, 4, 2, 3, 4, 6, 6, 6, 8, 6, 5, 6, 4, 5, 2, 4, 4, 4, 6, 4, 3, 4, 2, 3, 1, 3, 3, 3, 5, 3, 2, 3, 1, 2, 2, 4, 4, 4, 6, 4, 3, 4, 2, 3, 0

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn
• base

Comments

Number of endpoints: 0,8 - zero, 6,9 - one, 1,2,3,5,7 - two, 4 - four. - Michael B. Porter, Oct 28 2017

Examples

			The digit 1 has two endpoints, and the digit 8 has no endpoints, so a(18) = 2. - _Michael B. Porter_, Oct 28 2017
		

Links

• Paolo Xausa, Table of n, a(n) for n = 0..10000

Crossrefs

Cf. A027386, A027388, A027389, A055642, A100910, A102683, A268643.

Programs

Mathematica

A027387[n_] := Total[Map[{0, 2, 2, 2, 4, 2, 1, 2, 0, 1}[[#+1]] &, IntegerDigits[n]]];
Array[A027387, 100, 0] (* Paolo Xausa, Jul 16 2025 *)

PARI

a(n)=vecsum(apply(d->[0, 2, 2, 2, 4, 2, 1, 2, 0, 1][d+1], digits(n))); \\ based on program for A027386 by Andrew Howroyd, Michael B. Porter, Oct 26 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

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