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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. 4
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 if;

            end if;

        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

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Last modified May 11 03:49 EDT 2021. Contains 343784 sequences. (Running on oeis4.)