A129904 - OEIS

A129904

Find the first two terms in A003215, say A003215(i) and A003215(j), that are divisible by a number in A016921 not 1, say by k = A016921(m). Then i + j + 1 = k and k is added to the sequence.

7, 13, 19, 31, 37, 43, 49, 61, 67, 73, 79, 91, 97, 103, 109, 127, 133, 139, 151, 157, 163, 169, 181, 193, 199, 211, 217, 223, 229, 241, 247, 259, 271, 277, 283, 301, 307, 313, 331, 337, 343, 349, 361, 367, 373, 379, 397, 403, 409, 421, 427, 433, 439, 457, 463

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OFFSET

1,1

COMMENTS

Is this A004611 without the 1? - R. J. Mathar, Jul 16 2020

a(n) = A004611(n+1) for (at least) n <= 10^6. - Hugo Pfoertner, Oct 17 2020

LINKS

Table of n, a(n) for n=1..55.

EXAMPLE

A003215(1) = 7 is divisible by A016921(1) = 7, A003215(5) = 91 is divisible by A016921(1) = 7 and 5+1+1=7, so 7 is a member.

MAPLE

isA129904 := proc(k)

local i, j ;

if modp(k, 6) = 1 and k> 1 then

for i from 0 to k-1 do

j := k-1-i ;

if modp(A003215(i), k) =0 and modp(A003215(j), k) =0 then

return true;

end if;

end do:

false ;

else

false;

end if;

end proc:

for k from 1 to 400 do

if isA129904(k) then

printf("%d, ", k) ;

end if;

end do:

PROG

(PARI) isA129904(k)={my(a003215(n)=3*n*(n+1)+1); if(k%6!=1||k<=1, 0, for(i=0, k-1, my(j=k-1-i); if(a003215(i)%k==0&&a003215(j)%k==0, return(1)))); 0};

for(k=1, 500, if(isA129904(k), print1(k, ", "))) \\ Hugo Pfoertner, Oct 17 2020

CROSSREFS

Cf. A003215, A016921, A004611.

Sequence in context: A357277 A088513 A004611 * A133290 A038590 A218146

Adjacent sequences: A129901 A129902 A129903 * A129905 A129906 A129907

KEYWORD

nonn

AUTHOR

Mats Granvik, Jun 04 2007

EXTENSIONS

Extended by R. J. Mathar, Dec 16 2016

STATUS

approved