The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A344776 a(n) is the least prime p such that there are exactly n pairs of primes (q,r) with p > q > r such that q | r + p and r | q + p. 1
 2, 11, 7, 19, 103, 163, 263, 719, 3119, 3779, 6719, 18719, 7559, 67679, 52919, 181439, 138599, 241919, 818999, 262079, 453599, 665279, 1542239, 1713599, 1330559, 4979519, 2741759, 5569199, 7197119, 5745599 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS EXAMPLE a(3) = 19 because there are 3 pairs (3,2), (7,2), (11,3) with 3 | 2+19, 2 | 3+19, 7 | 2+19, 2 | 7+19, 11 | 3+19, 3 | 11+19. MAPLE M:= 10000: N:= ithprime(M): B:= Vector(N): a:= 1: do   a:= nextprime(a);   if a >= N then break fi;   b:= a;   do     b:= nextprime(b);     if b >= N then break fi;     c0:= chrem([-a, -b], [b, a]);     cs:= select(isprime, [seq(c0+i*a*b, i=ceil((b+2-c0)/(a*b)) .. floor((N-c0)/(a*b)))]);     B[cs]:= B[cs]+~1;   od: od: V:= Array(0..14): for i from 2 to N do   v:= A[i];   if V[v] = 0 then V[v]:= i fi od: convert(V, list); PROG (PARI) count_pairs(n) = my(i=0); forprime(q=1, n-1, forprime(r=1, q-1, if((r+n)%q==0 && (q+n)%r==0, i++))); i a(n) = forprime(p=1, , if(count_pairs(p)==n, return(p))) \\ Felix Fröhlich, May 28 2021 CROSSREFS Cf. A344788. Sequence in context: A306537 A170873 A224210 * A290572 A220771 A277055 Adjacent sequences:  A344773 A344774 A344775 * A344777 A344778 A344779 KEYWORD nonn,more AUTHOR J. M. Bergot and Robert Israel, May 28 2021 EXTENSIONS a(15)-a(17) from Chai Wah Wu, Jun 04 2021 a(18) from Bert Dobbelaere, Jun 07 2021 a(19)-a(21) from Chai Wah Wu, Jun 04 2021 a(22)-a(29) from Bert Dobbelaere, Jun 07 2021 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 5 23:38 EST 2021. Contains 349558 sequences. (Running on oeis4.)