Search: a131377 -id:a131377
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1, 2, 2, 3, 4, 4, 4, 5, 6, 7, 8, 8, 8, 9, 10, 11, 12, 12, 12, 13, 14, 15, 16, 16, 16, 16, 16, 16, 16, 17, 18, 18, 18, 18, 18, 18, 18, 19, 20, 21, 22, 22, 22, 23, 24, 25, 26, 26, 26, 26, 26, 26, 26, 27, 28, 29, 30, 31, 32, 32, 32, 33, 34, 35, 36, 37, 38, 38, 38, 38, 38, 39, 40, 40
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OFFSET
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0,2
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LINKS
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MAPLE
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P:=proc(n) local i, k, s; k:=1; s:=0; for i from 0 by 1 to n do if isprime(i) then if k=1 then k:=0; else k:=1; fi; fi; s:=s+k; print(s); od; end: P(100);
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PROG
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(PARI) a(n) = sum(m=0, n, (primepi(m) % 2) == 0) \\ Michel Marcus, Aug 15 2023
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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A131378
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Starting with 0, the sequence a(n) changes from 0 to 1 or back when the next number n is a prime.
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+10
3
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0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1
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OFFSET
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0,1
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COMMENTS
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LINKS
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EXAMPLE
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n = 0, 1, 2, 3, 4, 5, etc.
a(n)= 0, 0, 1, 0, 0, 1, etc.
Starting with 0 the sequence changes when we move from 1 to 2 because 2 is prime, again from 2 to 3 because also 3 is prime, then from 4 to 5 being 5 prime and so on.
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MAPLE
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P:=proc(n) local i, k; k:=0; for i from 0 by 1 to n do if isprime(i) then if k=1 then k:=0; else k:=1; fi; fi; print(k); od; end: P(100);
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MATHEMATICA
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nxt[{n_, a_}]:={n+1, Which[a==0&&PrimeQ[n+1], 1, a==1&&PrimeQ[n+1], 0, True, a]}; NestList[nxt, {0, 0}, 100][[All, 2]] (* Harvey P. Dale, Jul 19 2019 *)
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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