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1, 2, 4, 8, 32, 128, 512, 4096, 32768, 262144, 4194304, 67108864, 1073741824, 34359738368, 1099511627776, 35184372088832, 2251799813685248, 144115188075855872, 9223372036854775808, 1180591620717411303424, 151115727451828646838272
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refs;
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internal format)
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OFFSET
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0,2
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COMMENTS
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a(n)*a(n-4) = 2*a(n-1)*a(n-3) = a(n-1)*a(n-3) + c(n)*a(n-2)^2, where c(3*n+2) = 2, c(3*n) = c(3*n+1) = 1 for all n in Z. - Michael Somos, Oct 19 2018
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LINKS
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FORMULA
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a(n)=2^floor((n+1)(n+2)/6).
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EXAMPLE
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G.f. = 1 + 2*x + 4*x^2 + 8*x^3 + 32*x^4 + 128*x^5 + 512*x^6 + ... - Michael Somos, Oct 19 2018
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MATHEMATICA
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a[ n_] := 2^Quotient[ Binomial[n + 2, 2], 3]; (* Michael Somos, Oct 19 2018 *)
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PROG
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(PARI) {a(n) = 2^(binomial(n+2, 2)\3)}; /* Michael Somos, Oct 19 2018 */
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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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STATUS
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approved
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