OFFSET
1,3
COMMENTS
Every term with some permutations can become another term of this sequence.
The subsequence of primes begins: 3, 19, 37, 73, 91, 127...
The subsequence of triangular numbers begins: 1, 3, 6, 10, 15, 21, 28, 55...
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
If decimal expansion of n is x1 x2 ... xk then x1 + x2 + ... xk = T.
MATHEMATICA
TriangularQ[n_] := IntegerQ[Sqrt[1 + 8 n]]; Select[Range[0, 300], TriangularQ[Total[IntegerDigits[#]]] &] (* T. D. Noe, Jan 03 2013 *)
PROG
(Haskell)
a187744 n = a187744_list !! (n-1)
a187744_list = filter ((== 1) . a010054 . a007953) [0..]
-- Reinhard Zumkeller, Jan 03 2013
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Dario Piazzalunga, Jan 03 2013
STATUS
approved