A129457 - OEIS

A129457

a(1)=1; a(n) = number of earlier terms of the sequence that are coprime to (n+a(n-1)).

1, 1, 2, 2, 4, 2, 6, 2, 8, 2, 10, 2, 10, 2, 14, 2, 16, 2, 16, 2, 20, 2, 19, 23, 4, 4, 26, 4, 27, 26, 27, 31, 7, 33, 9, 27, 11, 35, 13, 39, 14, 13, 14, 16, 44, 9, 15, 33, 19, 38, 50, 11, 21, 37, 22, 11, 24, 24, 58, 24, 54, 24, 45, 63, 26, 25, 26, 27, 15, 60, 70, 29, 16, 14, 74, 14, 59

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..77.

EXAMPLE

13 + a(12) = 15. There are 10 terms among a(1),a(2)..,a(12) that are coprime to 15. (These terms are a(1),a(2),a(3),a(4),a(5),a(6),a(8),a(9), a(10) and a(12).) So a(13) = 10.

MAPLE

a[1]:=1: for n from 2 to 100 do ct:=0: for j from 1 to n-1 do if igcd(a[j], n+a[n-1])=1 then ct:=ct+1 else fi od: a[n]:=ct: od: seq(a[n], n=1..100); # Emeric Deutsch, Apr 17 2007

CROSSREFS

Cf. A129456.

Sequence in context: A137849 A316440 A118982 * A275365 A119655 A364949

Adjacent sequences: A129454 A129455 A129456 * A129458 A129459 A129460

KEYWORD

nonn

AUTHOR

Leroy Quet, Apr 16 2007

EXTENSIONS

More terms from Emeric Deutsch, Apr 17 2007

STATUS

approved