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 A052216 Sum of two powers of 10. 45
 2, 11, 20, 101, 110, 200, 1001, 1010, 1100, 2000, 10001, 10010, 10100, 11000, 20000, 100001, 100010, 100100, 101000, 110000, 200000, 1000001, 1000010, 1000100, 1001000, 1010000, 1100000, 2000000, 10000001, 10000010, 10000100, 10001000, 10010000, 10100000 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers n such that sum of digits is 2. A007953(a(n)) = 2; number of repdigits = #{2,11} = A242627(2) = 2. - Reinhard Zumkeller, Jul 17 2014 a(n) = 3*A237424(n) - 1. - Reinhard Zumkeller, Jan 28 2015 LINKS Vincenzo Librandi, T. D. Noe and R. Zumkeller, Table of n, a(n) for n = 1..10000 (first 48 terms from V. Librandi, up to 1036 from T. D. Noe) FORMULA Sum of two powers of 10: a(n) = 10^n + 10^m for n >= 0, m = 0..n. EXAMPLE The triangular array starts (see formula): 2, 11, 20, 101, 110, 200, 1001, 1010, 1100, 2000, 10001, 10010, 10100, 11000, 20000, 100001, 100010, 100100, 101000, 110000, 200000, 1000001, 1000010, 1000100, 1001000, 1010000, 1100000, 2000000, etc. - Bruno Berselli, Mar 07 2013 MATHEMATICA t = 10^Range[0, 9]; Select[Union[Flatten[Table[i + j, {i, t}, {j, t}]]], # <= t[[-1]] + 1 &] (* T. D. Noe, Oct 09 2011 *) With[{nn=7}, Sort[Join[Table[FromDigits[PadRight[{2}, n, 0]], {n, nn}], FromDigits/@Flatten[Table[Table[Insert[PadRight[{1}, n, 0], 1, i]], {n, nn}, {i, 2, n+1}], 1]]]] (* Harvey P. Dale, Nov 15 2011 *) Select[Range[10^9], Total[IntegerDigits[#]] == 2&] (* Vincenzo Librandi, Mar 07 2013 *) PROG (MAGMA) [n: n in [1..10100000] | &+Intseq(n) eq 2]; // Vincenzo Librandi, Mar 07 2013 (MAGMA) /* As a triangular array: */ [[10^n+10^m: m in [0..n]]: n in [0..8]]; // Bruno Berselli, Mar 07 2013 (Haskell) a052216 n = a052216_list !! (n-1) a052216_list = 2 : f [2] 9 where    f xs@(x:_) z = ys ++ f ys (10 * z) where                   ys = (x + z) : map (* 10) xs -- Reinhard Zumkeller, Jan 28 2015, Jul 17 2014 (PARI) a(n)=my(d=(sqrtint(8*n)-1)\2, t=n-d*(d+1)/2-1); 10^d + 10^t \\ Charles R Greathouse IV, Dec 19 2016 CROSSREFS Subsequence of A069263 and A107679. A038444 is a subsequence. Sums of n powers of 10: A011557 (1), A052217 (3), A052218 (4), A052219 (5), A052220 (6), A052221 (7), A052222 (8), A052223 (9), A052224 (10), A166311 (11), A235151 (12), A143164 (13), A235225(14), A235226 (15), A235227 (16), A166370 (17), A235228 (18), A166459 (19), A235229 (20). Cf. A007953, A242614, A242627, A237424. Sequence in context: A064975 A115095 A061907 * A094629 A081242 A071762 Adjacent sequences:  A052213 A052214 A052215 * A052217 A052218 A052219 KEYWORD easy,nonn,tabl AUTHOR Henry Bottomley, Feb 01 2000 STATUS approved

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Last modified January 20 17:05 EST 2019. Contains 319335 sequences. (Running on oeis4.)