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A060290 Primes which are sums of Twin Harshad numbers (includes overlaps). 1
3, 5, 7, 11, 13, 17, 19, 41, 223, 401, 419, 449, 881, 1021, 1259, 1289, 1471, 1601, 1607, 1871, 1999, 2029, 2281, 2549, 2609, 2833, 3041, 3359, 3457, 4001, 4049, 4481, 4801, 4931, 5641, 6329, 7499, 7561, 8081, 8849, 8929, 9613, 9619, 10111, 10321 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Table of n, a(n) for n=0..44.

FORMULA

{n in A000040:  (n-1)/2 in A005349 and (n+1)/2 in A005439}. - R. J. Mathar, Dec 20 2013

EXAMPLE

a(5)=17, a prime because the first Harshad number is 8 and the second is 9 and 8+9=17. In this sequence overlapping Harshad's are permitted: 1+2=3 and 2+3=5.

MAPLE

isA005349 := proc(n)

    if n mod digsum(n) = 0 then

        true;

    else

        false;

    end if;

end proc:

isA060290 := proc(n)

    local h1 ;

    if isprime(n) then

        h1 := (n-1)/2 ;

        if isA005349(h1) and isA005349(h1+1) then

            true;

        else

            false;

        end if;

    else

        false;

    end if;

end proc:

for n from 3 to 20000 do

    if isA060290(n) then

        printf("%d, ", n) ;

    end if;

end do: # R. J. Mathar, Dec 20 2013

PROG

(UBASIC)

20 A=0;

30 inc A;

40 if Ct=2 then Z=(A-1)+(A-2): if Z=prmdiv(Z) then print A-2; "+"; A-1; "="; Z; "/"; :inc Pt;

50 if Ct=2 then Ct=1:A=A-2;

60 X=1;

70 B=str(A);

80 L=len(B);

90 inc X;

100 S=mid(B, X, 1);

110 V=val(S):W=W+V;

120 if X<L then 90;

130 D=A/W:E=A\W: if D=E then inc Ct;

140 if Ct<>Dt+1 then Ct=0:Dt=0;

150 Dt=Ct:W=0;

160 if A<=10 then 30;

170 print Pt;

CROSSREFS

A060288, A060289, A005349, A060159.

Sequence in context: A264030 A070739 A061244 * A096880 A069458 A062280

Adjacent sequences:  A060287 A060288 A060289 * A060291 A060292 A060293

KEYWORD

easy,nonn,base

AUTHOR

Enoch Haga, Mar 24 2001

STATUS

approved

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Last modified July 21 06:55 EDT 2019. Contains 325192 sequences. (Running on oeis4.)