A111483 Triangular numbers all of whose digits are primes.

3, 55, 253, 325, 2775, 5253, 255255, 522753, 577275, 2235555, 2355535, 2532375, 3252525, 3352755, 7332535, 23273253, 25222753, 37372335, 55277355, 73235253, 222552253, 273253753, 325775575, 337337325, 577235253, 2373777253

Offset: 1

Author

Jonathan Vos Post, Nov 15 2005

Keywords

• base
• easy
• nonn

Comments

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?

Examples

			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).
		

Crossrefs

Intersection of A000217 and A046034.

Cf. A000040.

Programs

Mathematica

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 *)

Extensions

Corrected and extended by Robert G. Wilson v and Ray Chandler, Nov 18 2005