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A069970
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Numbers k such that sigma(reverse(k)) = sigma(reverse(k-1)) + sigma(reverse(k-2)).
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1
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3, 4, 352, 525, 532, 564, 572, 782, 3783, 5242, 5762, 5784, 7852, 7884, 31732, 38817, 41736, 46194, 52942, 57842, 61146, 63075, 67266, 68853, 95418, 196313, 403194, 424292, 436642, 444382, 493592, 521812, 521853, 521856, 523682, 527067, 527452, 541132, 543442
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OFFSET
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1,1
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LINKS
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EXAMPLE
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sigma(reverse(352)) = sigma(253) = 288 = 234 + 54 = sigma(153) + sigma(53) = sigma(reverse(352-1)) + sigma(reverse(352-2)).
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MATHEMATICA
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rev[n_] := FromDigits[Reverse[IntegerDigits[n]]]; Select[Range[3, 10^5], DivisorSigma[1, rev[ # ]] == DivisorSigma[1, rev[ # - 1]] + DivisorSigma[1, rev[ # - 2]] &]
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PROG
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(Python)
from itertools import count, islice
from sympy import divisor_sigma as sigma
def agen(): # generator of terms
dr2, dr1 = 1, 3
for k in count(3):
dr = sigma(int(str(k)[::-1]))
if dr == dr1 + dr2:
yield k
dr2, dr1 = dr1, dr
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CROSSREFS
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KEYWORD
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base,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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