A242383 Lesser of consecutive primes whose average is an oblong number.

5, 11, 29, 41, 53, 71, 239, 337, 419, 461, 503, 547, 599, 647, 863, 1051, 1187, 1481, 1721, 1801, 2549, 2647, 2969, 3539, 4421, 6317, 7129, 8009, 10301, 12653, 13567, 14033, 17291, 18353, 19181, 19457, 20021, 22943, 23561, 24179, 27059, 29063, 29753, 31151, 33301, 35153

Offset: 1

Author

Antonio Roldán, May 12 2014

Keywords

• nonn

Examples

			53 is in the sequence because it is prime, nextprime(53) = 59 and (53+59)/2 = 56 = 8*7, an oblong number.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002378, A154634, A263676.

Programs

Mathematica

f[n_] := NextPrime[n*(n + 1), -1] ; f /@ Select[Range[200], (ob =  #*(# + 1)) == (NextPrime[ob, -1] + NextPrime[ob])/2 &] (* Amiram Eldar, May 06 2020 *)
Select[Partition[Prime[Range[4000]],2,1],OddQ[Sqrt[1+4*Mean[#]]]&][[All,1]] (* Harvey P. Dale, Oct 25 2020 *)

PARI

{for(i=3,10^5,if(isprime(i),k=(i+nextprime(i+1))/4;if(issquare(8*k+1),print1(i,", "))))}