The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A101877 a(n) = k implies that there exists a set S of positive integers such that Sum_{ s_i in S } 1/s_i = n, max(S) = k and no set S' exists with the same sum and a smaller maximal element. 4
 1, 6, 24, 65, 184, 469, 1243, 3231 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS In other words, a(n) = min { max S | S subset of N*, Sum_{x in S} 1/x = n }. 8492 < a(9) <= 8507; 22788 < a(10) <= 22820; 60577 < a(11) <= 60639. - Hugo van der Sanden, Jan 20 2015 Little is known about the number of different sets S that achieve a(n). Paul Hanna asks if it is always true that a solution set S for n+1 must necessarily contain a solution set for n as a subset. This is true for small n, apparently, but seems to me unlikely to hold in general. - N. J. A. Sloane, Dec 31 2005 Martin and Shi show that it is not true for n = 5. They give a set that achieves a(6) without 136, while all sets that achieve a(5) include 136. - Matthieu Pluntz, Feb 20 2023 Does a(n+1) / a(n) converge? - David A. Corneth, Apr 08 2018 LINKS Table of n, a(n) for n=1..8. Greg Martin and Yue Shi, An algorithm for Egyptian fraction representations with restricted denominators, arXiv:2107.05076 [math.NT], 2021. Hugo van der Sanden, Perl and C code for this sequence. EXAMPLE The set S = { 1, 2, 3, 6 } gives a sum 1/1 + 1/2 + 1/3 + 1/6 = 2; exhaustive search shows that no set with a smaller maximal element can sum to 2, therefore a(2) = 6. a(1) = 1, S = { 1 } a(2) = 6, S = { 1 2 3 6 } a(3) = 24, S = { 1 2 3 4 5 6 8 9 10 15 18 20 24 } a(4) = 65, S = { 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 20 22 24 26 27 28 30 33 35 36 40 42 45 48 52 54 56 60 63 65 } a(5) = 184, using this set: { 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 30 32 33 34 35 36 38 39 40 42 44 45 48 50 51 52 54 55 56 58 60 62 63 65 66 68 69 70 72 75 76 77 78 80 81 84 85 87 88 90 91 92 93 95 96 99 102 104 105 108 110 112 114 115 116 117 126 130 133 136 138 140 143 144 145 150 152 153 154 155 156 161 162 165 168 170 171 174 175 176 180 184 } a(6) = 469, using the set: { 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 60 61 62 63 64 65 66 67 68 69 70 72 74 75 76 77 78 80 81 82 84 85 86 87 88 90 91 92 93 94 95 96 98 99 100 102 104 105 106 108 110 111 112 114 115 116 117 119 120 121 122 123 124 126 128 129 130 132 133 134 135 136 138 140 141 143 144 145 147 148 150 152 153 154 155 156 159 160 161 162 164 165 168 170 171 174 175 176 177 180 182 183 184 185 186 187 188 189 190 192 195 196 198 200 201 203 204 205 207 208 209 210 212 215 216 217 220 221 222 224 225 228 230 231 232 234 238 240 242 245 246 247 248 250 252 253 255 258 259 260 261 264 266 268 270 272 273 275 276 280 282 285 286 287 288 290 294 295 297 299 300 301 304 305 306 310 312 315 319 320 322 323 324 325 328 329 330 336 340 341 344 345 348 350 351 352 354 357 360 363 364 368 370 372 375 376 377 378 380 384 385 387 390 396 400 402 405 406 407 408 413 414 416 418 424 425 429 430 432 434 435 440 442 444 448 451 455 456 460 462 465 468 469 } CROSSREFS Cf. A002387. Sequence in context: A273358 A325517 A344508 * A270851 A092348 A274772 Adjacent sequences: A101874 A101875 A101876 * A101878 A101879 A101880 KEYWORD nonn,hard,nice,more AUTHOR Hugo van der Sanden, Jan 29 2005 EXTENSIONS Entry revised by N. J. A. Sloane, Dec 31 2005 Example for a(6) = 469 corrected by Hugo van der Sanden, Jan 31 2008 a(7)-a(8) from Hugo van der Sanden, Jan 20 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 5 05:37 EST 2023. Contains 367575 sequences. (Running on oeis4.)