login
List of pairs p, p+2 where p is prime and p and p+2 contain the same number of prime digits.
1

%I #13 Dec 04 2017 18:28:21

%S 3,5,5,7,13,15,23,25,29,31,43,45,53,55,73,75,83,85,89,91,103,105,109,

%T 111,113,115,163,165,173,175,193,195,223,225,229,231,233,235,263,265,

%U 283,285,293,295,313,315,353,355,373,375,383,385,389,391,409,411,433

%N List of pairs p, p+2 where p is prime and p and p+2 contain the same number of prime digits.

%C Prime digits are 2, 3, 5 or 7.

%t snpdQ[n_]:=Count[IntegerDigits[n],_?PrimeQ]==Count[IntegerDigits[n+2], _?PrimeQ]; {#,#+2}&/@Select[Prime[Range[100]],snpdQ]//Flatten (* _Harvey P. Dale_, Dec 04 2017 *)

%Y Cf. A077800.

%K nonn,base,less

%O 1,1

%A _Juri-Stepan Gerasimov_, Mar 15 2009

%E (13,15) inserted, (23,25) inserted, and all other numbers replaced by _R. J. Mathar_, May 19 2010

%E Definition changed to match the terms by _N. J. A. Sloane_, Dec 03 2017