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A091290 Numbers n such that sigma(n) + sigma(n+1) <= sigma(2*n+1). 6
1, 4, 7, 10, 13, 22, 31, 37, 46, 49, 52, 58, 61, 67, 73, 82, 85, 94, 97, 106, 112, 115, 121, 127, 130, 136, 142, 148, 157, 166, 172, 178, 181, 187, 193, 202, 211, 214, 217, 226, 229, 232, 238, 241, 247, 253, 256, 262, 274, 277, 283, 292, 298, 301, 307, 310, 313 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

MATHEMATICA

Do[s=(DivisorSigma[1, n]+DivisorSigma[1, n+1])/ DivisorSigma[1, 2*n+1]; If[ !Greater[s, 1], Print[n]], {n, 1, 10000000}]

PROG

(PARI) is(n)=sigma(n)+sigma(n+1)<=sigma(2*n+1) \\ Charles R Greathouse IV, Feb 14 2013

CROSSREFS

Cf. A000203, A091287-A091290.

Sequence in context: A002640 A096675 A069212 * A119256 A143454 A318774

Adjacent sequences:  A091287 A091288 A091289 * A091291 A091292 A091293

KEYWORD

nonn

AUTHOR

Labos Elemer, Feb 16 2004

EXTENSIONS

New name from Charles R Greathouse IV, Feb 14 2013

STATUS

approved

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Last modified July 23 11:44 EDT 2019. Contains 325254 sequences. (Running on oeis4.)