A268145 Twin prime pairs concatenated to their average in decimal representation (with the lesser twin prepended and the greater twin appended).

345, 567, 111213, 171819, 293031, 414243, 596061, 717273, 101102103, 107108109, 137138139, 149150151, 179180181, 191192193, 197198199, 227228229, 239240241, 269270271, 281282283, 311312313, 347348349, 419420421, 431432433, 461462463, 521522523, 569570571, 599600601

Offset: 1

Author

Mikk Heidemaa, Jan 27 2016

Keywords

• nonn
• base
• easy

Comments

The lesser prime of a twin prime pair is prepended and the greater prime is appended to their average (nonprime, interprime).

a(n) mod 3 = 0, (See A095958).

Examples

			a(1)=345: the lesser prime {3} of the first twin prime pair {3, 5} is prepended and the greater prime {5} is appended to their average {4}.
a(3)=111213: the lesser {11} of the 3rd twin prime pair {11, 13} is prepended and the greater prime {13} is appended to their average {12}.
		

Crossrefs

Cf. A001097, A014574, A095958, A111875.

Programs

Mathematica

UpToN[k_]:=FromDigits//@ StringJoin//@ ToString/@ {#-1, #, #+1} &/@ Select[ Table[ Prime[n]+1, {n, 2, PrimePi[k]}], PrimeQ[#+1] &]; UpToN[10000]