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A210470 Powerful numbers (A001694) which can be written as the sum of two relatively prime 3-powerful numbers different from 1. 0
841, 968, 2312, 3528, 5041, 5776, 12769, 14884, 16641, 45125, 51984, 109561, 123823, 157609, 168921, 207576, 373321, 450241, 498436, 609725, 711828, 731025, 798768 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

REFERENCES

Jean-Marie de Konninck, Those Fascinating Numbers, Amer. Math. Soc., 2009.

Alonso Del Arte, Posting to the Sequence Fans Mailing List, Mar 10 2011.

LINKS

Table of n, a(n) for n=1..23.

FORMULA

{ a in A001694: a=b+c and b,c >1 and b,c in A036966 and gcd(b,c)=1}. - R. J. Mathar, May 01 2013

EXAMPLE

841 = 216+625 ; 968 = 343+625 ; 2312=125+2187;

MAPLE

isA210470 := proc(n)

    if isA001694(n) then

        for i from 2 do

            p3 := A036966(i) ;

            if p3+2 > n then

                return false;

            end if;

            p3comp := n-p3 ;

            if isA036966(p3comp) and igcd(p3, p3comp) = 1 then

                # print(n, p3, p3comp) ;

                return true;

            end if;

        end do:

        return false;

    else

        return false;

    end if;

end proc:

for n from 1 do

    if isA210470(n) then

        printf("%d, ", n) ;

    end if;

end do: # R. J. Mathar, May 01 2013

CROSSREFS

Sequence in context: A269894 A252780 A159690 * A108324 A133496 A253599

Adjacent sequences:  A210467 A210468 A210469 * A210471 A210472 A210473

KEYWORD

nonn,more

AUTHOR

N. J. A. Sloane, Apr 22 2013

STATUS

approved

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Last modified January 17 14:57 EST 2020. Contains 330958 sequences. (Running on oeis4.)