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A217704 Smallest number k > n for which sigma(k-n) = sigma(k+n). 1
34, 53, 23, 19, 26, 41, 31, 38, 49, 52, 68, 82, 112, 80, 103, 76, 110, 123, 166, 83, 101, 136, 219, 164, 130, 186, 147, 133, 381, 254, 208, 149, 253, 169, 131, 246, 172, 332, 404, 166, 245, 312, 148, 209, 309, 241, 487, 328, 217, 260 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sigma() in the definition is the sum-of-divisors function A000203.

LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..10000

EXAMPLE

a(26)=186 because sigma(186-26)=sigma(160)=378=sigma(212)=sigma(186+26) and there is no k such that 26<k<186 for which sigma(k-26)=sigma(k+26).

MATHEMATICA

Table[Min[Select[Range[500], DivisorSigma[1, # - n] == DivisorSigma[1, # + n] && # > n &]], {n, 50}]

PROG

(PARI) a(n)={my(k=n+1); while(sigma(k-n)<>sigma(k+n), k++); k} \\ Andrew Howroyd, Feb 25 2018

CROSSREFS

Cf. A217768.

Sequence in context: A214473 A092888 A217768 * A274380 A305061 A051969

Adjacent sequences:  A217701 A217702 A217703 * A217705 A217706 A217707

KEYWORD

nonn

AUTHOR

Jayanta Basu, Mar 26 2013

STATUS

approved

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Last modified October 16 05:35 EDT 2019. Contains 328044 sequences. (Running on oeis4.)