A165929 -id:A165929 - cp's OEIS frontend

A081973 a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.

1, 2, 5, 11, 23, 47, 95, 215, 479, 959, 2063, 4127, 8255, 19007, 38327, 76655, 168647, 338663, 708263, 1453823, 3308543, 7154303, 14919599, 29910119, 59820239, 119676959, 239387375, 538142975, 1205440295, 2651968655, 6663140495

Offset: 1

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Amarnath Murthy, Apr 03 2003

nonn

a(n+1)/a(n) >= 2 for all n. Is a(n+1)/a(n) bounded? Up to n=160, the maximum value is a(31)/a(30)=2.5125261124174184479... - Benoit Cloitre, Apr 17 2003
a(n) == 23 (mod 24) for all n>=5. - Dean Hickerson, Apr 20 2003
a(n) = partial sums of A165929(n). [From Jaroslav Krizek, Sep 30 2009]

T. D. Noe, Table of n, a(n) for n=1..200

a[1]=1; a[n_] := a[n]=a[n-1]+DivisorSigma[1, a[n-1]]

More terms from Gabriel Cunningham (gcasey(AT)mit.edu), Apr 07 2003

cp's OEIS Frontend

A081973 a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.

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