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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.
0
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
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
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
KEYWORD
nonn
AUTHOR
Mats Granvik, Jun 04 2007
EXTENSIONS
Extended by R. J. Mathar, Dec 16 2016
STATUS
approved