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A081973 a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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]

LINKS

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

MAPLE

with(numtheory); P:=proc(q) local a, b, n; a:=1; print(a);

for n from 1 to q do b:=a+sigma(a); print(b); a:=b; od; print(); end: P(40); # Paolo P. Lava, Jul 31 2013

MATHEMATICA

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

CROSSREFS

Sequence in context: A083329 A055010 A266550 * A334276 A055496 A105120

Adjacent sequences:  A081970 A081971 A081972 * A081974 A081975 A081976

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Apr 03 2003

EXTENSIONS

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

STATUS

approved

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Last modified November 28 06:42 EST 2021. Contains 349401 sequences. (Running on oeis4.)