OFFSET
1,1
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?
EXAMPLE
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).
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 *)
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Jonathan Vos Post, Nov 15 2005
EXTENSIONS
Corrected and extended by Robert G. Wilson v and Ray Chandler, Nov 18 2005
STATUS
approved