A024612 - OEIS

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A024612

a(n) = number in position n when all i^2 - i*j + j^2, where 1 <= i < j are arranged in increasing order.

3, 7, 7, 12, 13, 13, 19, 19, 21, 21, 27, 28, 28, 31, 31, 37, 37, 39, 39, 43, 43, 48, 49, 49, 52, 52, 57, 57, 61, 61, 63, 63, 67, 67, 73, 73, 75, 76, 76, 79, 79, 84, 84, 91, 91, 91, 91, 93, 93, 97, 97, 103, 103, 108, 109, 109, 111, 111, 112, 112, 117, 117, 124, 124, 127, 127, 129, 129, 133

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Table of n, a(n) for n=1..69.

MAPLE

A024612 := proc(n)

local i, j, disc;

# n=i^2+j^2-i*j = (j-i)^2+i*j, 1<=i<j

# so (j-i)>=1 and i*j>=j and i^2+j^2-i*j >= 1+j max search radius

for j from 2 to n-1 do

# i=(j +- sqrt(4n-3j^2))/2

disc := 4*n-3*j^2 ;

if disc >= 0 then

if issqr(disc) then

i := (j+sqrt(disc))/2 ;

if type(i, 'integer') and i >= 1 and i<j then

printf("%d, ", n) ;

end if;

if disc > 0 then

i := (j-sqrt(disc))/2 ;

if type(i, 'integer') and i >= 1 and i<j then

printf("%d, ", n) ;

end if;

end do:

end proc:

for t from 1 to 120 do

A024612(t);

end do: # R. J. Mathar, Aug 21 2016

CROSSREFS

Sequence in context: A080457 A119644 A109386 * A227025 A073881 A137315

Adjacent sequences: A024609 A024610 A024611 * A024613 A024614 A024615

KEYWORD

nonn

AUTHOR

Clark Kimberling

STATUS

approved