OFFSET
1,2
COMMENTS
a(23) = 60755428490.
No more terms below 10^11.
EXAMPLE
The elements of the continued fractions of the harmonic mean of the divisors of the terms are:
n a(n) elements
-- ----------- -------------------------------------------
1 1 1
2 15 2,2
3 8 2,7,2
4 545 3,3,3,3
5 21 2,1,1,1,2
6 1131 5,2,1,1,2,5
7 16 2,1,1,2,1,1,2
8 98124 17,1,1,3,3,1,1,17
9 28676 6,1,2,3,1,3,2,1,6
10 1109305 6,1,1,1,1,1,1,1,1,6
11 28672 11,2,1,1,1,10,1,1,1,2,11
12 16837500 24,1,1,1,2,1,1,2,1,1,1,24
13 1231932 18,1,1,1,1,1,8,1,1,1,1,1,18
14 477021580 38,2,3,1,1,1,1,1,1,1,1,3,2,38
15 6129711 14,2,2,1,1,1,1,9,1,1,1,1,2,2,14
16 734420331 20,2,1,1,1,1,1,1,1,1,1,1,1,1,2,20
17 441972042 15,1,3,2,2,1,1,2,15,2,1,1,2,2,3,1,15
18 4343866215 18,1,1,7,1,8,2,1,1,1,1,2,8,1,7,1,1,18
19 42741916965 94,1,1,7,4,1,1,1,1,3,1,1,1,1,4,7,1,1,94
20 96692841558 28,2,4,1,1,4,1,1,1,6,6,1,1,1,4,1,1,4,2,28
21 2193739177 19,1,1,1,3,1,1,1,1,1,9,1,1,1,1,1,3,1,1,1,19
MATHEMATICA
cfhm[n_] := ContinuedFraction[DivisorSigma[0, n]/DivisorSigma[-1, n]]; seq[len_, nmax_] := Module[{s = Table[0, {len}], c = 0, n = 1, i, cf}, While[c < len && n < nmax, cf = cfhm[n]; If[PalindromeQ[cf] && (i = Length[cf]) <= len && s[[i]] == 0, c++; s[[i]] = n]; n++]; TakeWhile[s, # > 0 &]]; seq[11, 10^7]
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Nov 19 2021
STATUS
approved