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 A023689 Numbers with exactly 7 ones in binary expansion. 18
 127, 191, 223, 239, 247, 251, 253, 254, 319, 351, 367, 375, 379, 381, 382, 415, 431, 439, 443, 445, 446, 463, 471, 475, 477, 478, 487, 491, 493, 494, 499, 501, 502, 505, 506, 508, 575, 607, 623, 631, 635, 637, 638, 671, 687 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Ivan Neretin, Table of n, a(n) for n = 1..10000 Robert Baillie, Summing the curious series of Kempner and Irwin, arXiv:0806.4410 [math.CA], 2008-2015. See p. 18 for Mathematica code irwinSums.m. M. I. Mazurkov and A. V. Sokolov, Nonlinear substitution S-boxes based on composite power residue codes, Radioelectronics and Communications Systems, Vol. 56, No. 9 (2013). DOI: 10.3103/S0735272713090045. FORMULA a(n+1) = A057168(a(n)). - M. F. Hasler, Aug 27 2014 Sum_{n>=1} 1/a(n) = 1.386779022721502147026318489565477811900220906277367947393004721391094590038... (calculated using Baillie's irwinSums.m, see Links). - Amiram Eldar, Feb 14 2022 MATHEMATICA Select[ Range[ 127, 704 ], (Count[ IntegerDigits[ #, 2 ], 1 ]==7)& ] PROG (PARI) is_A023689(n)=hammingweight(n)==7 \\ M. F. Hasler, Aug 27 2014 (PARI) print1(t=2^7-1); for(i=2, 50, print1(", "t=A057168(t))) \\ M. F. Hasler, Aug 27 2014 CROSSREFS Cf. A000079, A018900, A014311, A014312, A014313, A023688, A023690, A023691 (Hamming weight = 1, 2, ..., 9), A057168. Sequence in context: A137985 A065092 A141916 * A095284 A127579 A107380 Adjacent sequences: A023686 A023687 A023688 * A023690 A023691 A023692 KEYWORD nonn,base,easy AUTHOR STATUS approved

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Last modified November 29 06:59 EST 2022. Contains 358422 sequences. (Running on oeis4.)