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#55 by Sean A. Irvine at Sat Mar 25 15:27:11 EDT 2023
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#54 by Joerg Arndt at Sun Mar 05 09:42:06 EST 2023
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Discussion
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| Sun Mar 05
| 12:19
| Michel Marcus: something is wrong here j=1)+2^i+2^j)
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#53 by Joerg Arndt at Sun Mar 05 09:41:48 EST 2023
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| PROG
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(PARI) N=41; B(x)={nB=floor(log(x)/log(2)); z=0;
for(i=0, nB, if(bittest(x, i), z++; if(z>3, return(0); ); ); );
if(z == 3, return(1); , return(0); ); };
x=6; while(N, x=nextprime(x); if(B(x), print1(x, ", "); N--; ); x++; ); \\ Washington Bomfim, Jan 11 2011
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| STATUS
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proposed
editing
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#52 by Michel Marcus at Sat Mar 04 03:45:33 EST 2023
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#51 by Michel Marcus at Sat Mar 04 03:45:27 EST 2023
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| LINKS
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Richard Ehrenborg and N. Bradley Fox, <a href="http://arxiv.org/abs/1408.6858">The Descent Set Polynomial Revisited</a>, arXiv:1408.6858, [math.CO], 2014.
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#50 by Jon E. Schoenfield at Fri Mar 03 20:04:12 EST 2023
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| EXAMPLE
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7 = 2^2 + 2^1 + 1
11 = 2^3 + 2^1 + 1
13 = 2^3 + 2^2 + 1
19 = 2^4 + 2^1 + 1
37 = 2^5 + 2^2 + 1
41 = 2^5 + 2^3 + 1
67 = 2^6 + 2^1 + 1
73 = 2^6 + 2^3 + 1
97 = 2^6 + 2^5 + 1
131 = 2^7 + 2^1 + 1
137 = 2^7 + 2^3 + 1
193 = 2^7 + 2^6 + 1
521 = 2^9 + 2^3 + 1
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#49 by M. F. Hasler at Fri Mar 03 19:07:52 EST 2023
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#48 by M. F. Hasler at Fri Mar 03 19:02:30 EST 2023
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| PROG
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(PARI) A81091=[7]; (]; next_A081091(p, i=exponent(p), j=exponent(p-2^i))=!until(isprime(2^i+2^j+1), j++>=i && i++ && j=1)+2^i+2^j); )
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#47 by M. F. Hasler at Fri Mar 03 19:01:02 EST 2023
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| COMMENTS
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A000120(a(n))=3.
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| FORMULA
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A000120(a(n)) = 3.
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| PROG
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(PARI) N=41; ; B(x)={nB=floor(log(x)/log(2)); z=0;
(PARI) A81091=[7]; (next_A081091(p, i=exponent(p), j=exponent(p-2^i))=!until(isprime(2^i+2^j+1), j++>=i && i++ && j=1)+2^i+2^j);
A081091(n)={for(k=#A81091, n-1, A81091=concat(A81091, next_A081091(A81091[k]))); A81091[n]} \\ M. F. Hasler, Mar 03 2023
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| STATUS
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approved
editing
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#46 by Joerg Arndt at Wed Jul 20 01:31:25 EDT 2022
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