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A104589
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a(1)=1. a(n) = a(n-1) + (sum of terms, from among terms a(1) through a(n-1), which are prime or 1).
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4
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1, 2, 5, 13, 34, 55, 76, 97, 215, 333, 451, 569, 1256, 1943, 2630, 3317, 4004, 4691, 10069, 25516, 40963, 56410, 71857, 87304, 102751, 118198, 133645, 149092, 164539, 179986, 195433, 210880, 226327, 241774, 257221, 529889, 802557, 1075225
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OFFSET
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1,2
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COMMENTS
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By Dirichlet's Theorem there are an infinite number of primes in this sequence.
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LINKS
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FORMULA
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a(n) = 3*a(n-1) - a(n-2) if a(n-1) is prime, else a(n) = 2*a(n-1) - a(n-2) for n>3. - John Tyler Rascoe, Jul 20 2022
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EXAMPLE
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The noncomposites among the first 8 terms of the sequence are 1, 2, 5, 13 and 97. The sum of these is 1+2+5+13+97 = 118. So a(9) = a(8) + 118 = 215.
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MATHEMATICA
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f[lst_] := Append[lst, Last@ lst + Plus @@ Select[lst, (PrimeQ@ # || # == 1) &]]; Nest[f, {1}, 38] (* Robert G. Wilson v, Jul 02 2007 *)
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PROG
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(PARI) lista(nn) = my(va = vector(nn), s = 1); va[1] = 1; for (n=2, nn, va[n] = va[n-1] + s; if (isprime(va[n]), s += va[n]); ); va; \\ Michel Marcus, Jul 21 2022
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CROSSREFS
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KEYWORD
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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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