A196440 a(n) = the sum of numbers k <= n such that GCQ_A(n, k) >= 2 (see definition in comments).

0, 0, 3, 4, 12, 11, 25, 30, 38, 49, 63, 63, 88, 99, 113, 130, 150, 161, 187, 198, 224, 247, 273, 285, 322, 345, 371, 400, 432, 455, 493, 522, 554, 589, 627, 651, 700, 735, 773, 808, 858, 893, 943, 984, 1028, 1075, 1125, 1161, 1222, 1269, 1319, 1372, 1428, 1475, 1537, 1590, 1646, 1705, 1767, 1802, 1888, 1947, 2009, 2074, 2142, 2201, 2275

Offset

1,3

Comments

Definition of GCQ_A: The greatest common non-divisor of type A (GCQ_A) of two positive integers a and b (a<=b) is the largest positive non-divisor q of numbers a and b such that 1<=q<=a common to a and b; GCQ_A(a, b) = 0, if no such c exists.

GCQ_A(1, b) = GCQ_A(2, b) = 0 for b >=1. GCQ_A(a, b) = 0 or >= 2.

a(n) is also the sum of number k <= n such that LCQ_A(n, k) >= 2.

Definition of LCQ_A: The least common non-divisor of type A (LCQ_A) of two positive integers a and b (a<=b) is the least positive non-divisor q of numbers a and b such that 1<=q<=a common to a and b; LCQ_A(a, b) = 0 if no such c exists.

LCQ_A(1, b) = LCQ_A(2, b) = 0 for b >=1. LCQ_A(a, b) = 0 or >= 2.

Links

Antti Karttunen, Table of n, a(n) for n = 1..1001

Formula

a(n) = A000217(n) - A196439(n).

Example

For n = 6, a(6) = 11 because there are 2 cases k (k = 5, 6) with GCQ_A(6, k) >= 2:
GCQ_A(6, 1) = 0, GCQ_A(6, 2) = 0, GCQ_A(6, 3) = 0, GCQ_A(6, 4) = 0, GCQ_A(6, 5) = 4, GCQ_A(6, 6) = 5. Sum of such numbers k is 11.
Also there are 2 same cases k  with LCQ_A(6, k) >= 2:
LCQ_A(6, 1) = 0, LCQ_A(6, 2) = 0, LCQ_A(6, 3) = 0, LCQ_A(6, 4) = 0, LCQ_A(6, 5) = 4, LCQ_A(6, 6) = 4.

Prog

(PARI)
GCQ_A(a, b) = { forstep(m=min(a, b)-1, 2, -1, if(a%m && b%m, return(m))); 0; }; \\ From PARI-program in A196438
A196440(n) = sum(k=1, n, (2<=GCQ_A(n, k))*k); \\ Antti Karttunen, Jun 12 2018

Crossrefs

Cf. A196437, A196438, A196439, A196441, A196442, A196443, A196444.

Sequence in context: A164982 A081837 A348996 * A101404 A067327 A346470

Adjacent sequences: A196437 A196438 A196439 * A196441 A196442 A196443

Keyword

nonn

Author

Jaroslav Krizek, Nov 26 2011

Extensions

More terms from Antti Karttunen, Jun 12 2018

Status

approved