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 A227758 a(n) = sigma(sigma(n)) - sigma(n) - n, where sigma(n) = A000203(n) = sum of the divisors of n. 4
 -1, -1, 0, -3, 1, 10, 0, 1, -8, 11, 5, 16, -3, 22, 21, -15, 4, -1, 3, 34, 10, 33, 13, 84, -24, 28, 23, 36, 13, 93, 0, 9, 43, 32, 41, -15, -15, 70, 25, 104, 13, 114, -3, 96, 45, 77, 29, 52, -26, -15, 72, 21, 13, 186, 68, 184, 49, 86, 49, 252, -27, 94, 43, -63 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Conjecture: a(n) = 0 for Mersenne primes (A000668). [This is easily proved: For Mersenne primes n=2^p-1, sigma(n)=n+1=2^p, sigma(2^p)=2^(p+1)-1, thus a(n)=0. - M. F. Hasler, Jul 30 2013] a(n) <  0 for numbers n from A227759, a(n) >  0 for numbers n from A227760. Sequence contains anomalous increased frequency of values 13 (see A227756). LINKS Paul Tek, Table of n, a(n) for n = 1..10000 FORMULA a(n) = A051027(n) - A000203(n) - n. EXAMPLE For n = 6; a(n) = sigma(sigma(6)) - sigma(6) - 6 = 28 - 12 - 6 = 10. CROSSREFS Cf. A051027, A000203, A000668, A227759, A227760, A227756. Sequence in context: A128415 A227795 A090479 * A304638 A141903 A010289 Adjacent sequences:  A227755 A227756 A227757 * A227759 A227760 A227761 KEYWORD sign AUTHOR Jaroslav Krizek, Jul 26 2013 STATUS approved

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Last modified November 26 09:38 EST 2020. Contains 338639 sequences. (Running on oeis4.)