A076667 - OEIS

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A076667

antisigma(n) + antisigma(n+3) = antisigma(n+1) + antisigma(n+2), where antisigma(n) = sum of the non-divisors of n that are between 1 and n.

6, 907, 1359, 2512, 26545, 6094105, 10714840, 11967486, 36282316, 45123265, 60144196, 113547460, 318424060, 474656416, 488176150, 920250976, 927186976, 993590680, 2509123036, 3015854296, 3966424141, 4168017460, 4360145356

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OFFSET

1,1

COMMENTS

Each term of the sequence marks the start of four consecutive antisigma-values for which the sum of the means equals the sum of the extremes.

LINKS

Table of n, a(n) for n=1..23.

EXAMPLE

antisigma(6) + antisigma(9) = 9 + 32 = 41; antisigma(7) + antisigma(8) = 20 + 21 = 41, so 6 is a term of the sequence.

MATHEMATICA

antisigma[n_] := (n (n + 1) / 2) - DivisorSigma[1, n]; Select[Range[10^5], antisigma[ # ] + antisigma[ # + 3] == antisigma[ # + 1] + antisigma[ # + 2] &]

CROSSREFS

Sequence in context: A180992 A229629 A137801 * A000652 A214638 A175554

Adjacent sequences: A076664 A076665 A076666 * A076668 A076669 A076670

KEYWORD

nonn

AUTHOR

Joseph L. Pe, Oct 25 2002

EXTENSIONS

a(6)-a(23) from Donovan Johnson, Dec 02 2009

STATUS

approved