This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A078426 Numbers n such that there is no solution to the equation sigma(x)=2^n, where sigma(x) denotes the sum of the divisors of x. 12
 1, 4, 6, 11, 470, 475, 477, 480, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520, 522, 525, 527, 532, 1077, 1082 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers that are not a sum of distinct Mersenne exponents (A000043). - Vladeta Jovovic, Jan 01 2003 Because there is a large gap between the 31st and 32nd Mersenne exponents, all n between 704338 and 756839 are in this sequence. - T. D. Noe, Oct 12 2006 A000203(A180162(a(n))) = 6^a(n), for n>1. - Walter Kehowski, Aug 16 2010 Using all known Mersenne exponents, there are exactly 52935 terms in this sequence. When a new Mersenne prime (with exponent q) is found, there will be no new terms if the sum of the previous Mersenne exponents (A109472) is greater than q - 22. REFERENCES S. Kravitz, "Beware of the Fifth", Solution to Problem 2309, Journal of Recreational Mathematics, 29(1):76 Baywood NY 1998. LINKS T. D. Noe, Table of n, a(n) for n=1..300 EXAMPLE a(2)=4 because no positive integer value of x can satisfy sigma(x)=2^4=16. MATHEMATICA e={2, 3, 5, 7, 13, 17, 19, 31, 61, 89, 107, 127, 521, 607, 1279, 2203, 2281, 3217, 4253, 4423, 9689, 9941, 11213, 19937, 21701, 23209, 44497, 86243, 110503, 132049, 216091, 756839, 859433, 1257787, 1398269}; u={0}; Do[u=Union[u, u+e[[k]]], {k, Length[e]}]; Complement[Range[e[[-1]]], u] CROSSREFS Cf. A000203, A007369, A046528, A063883, A180221 (complement). Sequence in context: A105308 A116983 A196271 * A212558 A293836 A278252 Adjacent sequences:  A078423 A078424 A078425 * A078427 A078428 A078429 KEYWORD nonn AUTHOR Shyam Sunder Gupta, Dec 29 2002 EXTENSIONS More terms from Vladeta Jovovic, Jan 01 2003 Edited by N. J. A. Sloane, Aug 23 2010 Edited by Max Alekseyev, Jan 24 2014 STATUS approved

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

Last modified March 23 18:13 EDT 2019. Contains 321433 sequences. (Running on oeis4.)