A111483 - OEIS

%I #8 Oct 31 2013 12:17:32

%S 3,55,253,325,2775,5253,255255,522753,577275,2235555,2355535,2532375,

%T 3252525,3352755,7332535,23273253,25222753,37372335,55277355,73235253,

%U 222552253,273253753,325775575,337337325,577235253,2373777253

%N Triangular numbers all of whose digits are primes.

%C 3 = T(2) and 253 = T(22) have all prime digits and all prime digits in their indices as triangular numbers. What is the next of this subsequence?

%e 3 = T(2), 55 = T(10), 253 = T(22), 325 = T(25), 2775 = T(74), 5253 = T(102), 255255 = T(714), 522753 = T(1022), 577275 = T(1074), 2235555 = T(2114), 2355535 = T(2170), 2532375 = T(2250).

%t fQ[n_] := Union@Join[{2, 3, 5, 7}, IntegerDigits[n(n + 1)/2]] == {2, 3, 5, 7}; s = Select[ Range[10^5], fQ[ # ] &]; s (s + 1)/2 (* _Robert G. Wilson v_ *)

%Y Intersection of A000217 and A046034.

%Y Cf. A000040.

%K base,easy,nonn

%O 1,1

%A _Jonathan Vos Post_, Nov 15 2005

%E Corrected and extended by _Robert G. Wilson v_ and _Ray Chandler_, Nov 18 2005