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A052462
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a(n) is the minimal positive integral solution k to 24*k == 1 (mod 5^n).
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6
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4, 24, 99, 599, 2474, 14974, 61849, 374349, 1546224, 9358724, 38655599, 233968099, 966389974, 5849202474, 24159749349, 146230061849, 603993733724, 3655751546224, 15099843343099, 91393788655599, 377496083577474
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OFFSET
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1,1
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COMMENTS
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Related to a Ramanujan congruence for the partition function P = A000041.
Extending work of Ramanujan, Watson (1938) proved that P(m) == 0 (mod 5^n) if 24*m == 1 (mod 5^n). In particular, P(a(n)) == 0 (mod 5^n). - Petros Hadjicostas, Jul 29 2020
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LINKS
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FORMULA
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G.f.: x*(-25*x^2 + 20*x + 4)/((1 - x)*(1 - 5*x)*(1 + 5*x)).
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EXAMPLE
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A000041(a(4)) = A000041(599) = 435350207840317348270000 == 0 (mod 5^4). (End)
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MATHEMATICA
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Table[PowerMod[24, -1, 5^a], {a, 21}]
CoefficientList[Series[(-25x^2+20x+4)/((1-x)(1-5x)(1+5x)), {x, 0, 30}], x] (* Vincenzo Librandi, Jul 01 2012 *)
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PROG
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(Magma) I:=[4, 24, 99]; [n le 3 select I[n] else Self(n-1)+25*Self(n-2)-25*Self(n-3): n in [1..30]]; // Vincenzo Librandi, Jul 01 2012
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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