A131346 a(1)=1; a(n) = a(n-1) + (number of the terms, from among terms a(1) through a(n-1), which are coprime to Sum_{k=1..n-1} a(k)).

1, 2, 4, 7, 8, 10, 12, 14, 16, 18, 20, 21, 30, 43, 47, 62, 70, 80, 89, 95, 115, 123, 145, 152, 162, 172, 179, 206, 234, 263, 270, 276, 286, 298, 307, 333, 341, 376, 404, 439, 449, 489, 507, 537, 557, 602, 635, 655, 690, 725, 749, 787, 812, 838, 863, 905, 920, 941

Offset

1,2

Links

Table of n, a(n) for n=1..58.

Example

The sum of the first 12 terms of the sequence is 133 = 7*19.
There are 9 terms from among the first 12 terms of the sequence that are coprime to 133 (a(1)=1, a(2)=2, a(3)=4, a(5)=8, a(6)=10, a(7)=12, a(9)=16, a(10)=18, a(11)=20). So a(13)= a(12) + 9 = 30.

Maple

a[1] := 1; for n from 2 to 60 do ct := 0; for j to n-1 do if gcd(a[j], sum(a[i], i = 1 .. n-1)) = 1 then ct := ct+1 else ct := ct end if end do; a[n] := a[n-1]+ct end do; seq(a[n], n = 1 .. 60) # Emeric Deutsch, Jul 17 2007

Crossrefs

Cf. A131347.

Sequence in context: A127875 A056231 A248637 * A341350 A047540 A116478

Adjacent sequences: A131343 A131344 A131345 * A131347 A131348 A131349

Keyword

nonn

Author

Leroy Quet, Jul 01 2007

Extensions

More terms from Emeric Deutsch and Joshua Zucker, Jul 17 2007

Status

approved