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A055812
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a(n) and floor(a(n)/5) are both squares; i.e., squares which remain squares when written in base 5 and last digit is removed.
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20
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0, 1, 4, 9, 49, 81, 324, 2209, 15129, 25921, 103684, 710649, 4870849, 8346321, 33385284, 228826129, 1568397609, 2687489281, 10749957124, 73681302249, 505019158609, 865363202001, 3461452808004
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OFFSET
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1,3
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COMMENTS
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For the first 3 terms, the above "base 5" interpretation is questionable, since they have only 1 digit in base 5. It is understood that dropping this digit yields 0. - M. F. Hasler, Jan 15 2012
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LINKS
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Table of n, a(n) for n=1..23.
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FORMULA
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Empirical g.f.: -x^2*(9*x^11 +49*x^10 +324*x^9 +81*x^8 -698*x^7 -698*x^6 -968*x^5 -242*x^4 +49*x^3 +9*x^2 +4*x +1) / ((x -1)*(x +1)*(x^2 -4*x -1)*(x^2 +1)*(x^2 +4*x -1)*(x^4 +18*x^2 +1)). - Colin Barker, Sep 15 2014
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EXAMPLE
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a(4) = 49 because 49 = 7^2 = 144 base 5 and 14 base 5 = 9 = 3^2.
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PROG
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(PARI) b=5; for(n=1, 2e9, issquare(n^2\b) && print1(n^2, ", ")) \\ M. F. Hasler, Jan 15 2012
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CROSSREFS
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For analogs in other bases see A055792 (base 2), A055793 (base 3), A055808 (base 4), A055851 (base 6), A204517 (base 7), A204512 (base 8), A204503 (base 9) and A023110 (base 10).
Squares of A204520. The square roots of floor[a(n)/5] are given in A204521.
Sequence in context: A115711 A029791 A053961 * A268099 A061867 A019544
Adjacent sequences: A055809 A055810 A055811 * A055813 A055814 A055815
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KEYWORD
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base,nonn
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AUTHOR
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Henry Bottomley, Jul 14 2000
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EXTENSIONS
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More terms added and offset changed to 1 by M. F. Hasler, Jan 15 2012
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STATUS
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approved
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