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A072060
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Smallest prime p such that 2*p+1 has n prime factors (with multiplicity).
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4
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2, 7, 13, 67, 283, 607, 1093, 12757, 22963, 49207, 482233, 1623847, 797161, 14614627, 19929037, 35872267, 150663523, 2044719247, 1355971711, 9879222469, 37773497677, 200490103057, 172595827849, 235357947067, 1176789735337, 5507375961379, 10591107618037
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OFFSET
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1,1
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LINKS
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EXAMPLE
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a(4)=67=A000040(19): 2*67+1 = 135 = 5*3^3, 4 factors.
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PROG
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(PARI)
generate(A, B, n) = A=max(A, 2^n); (f(m, p, n) = my(list=List()); if(n==1, forprime(q=max(p, ceil(A/m)), B\m, my(t=m*q); if(isprime((t-1)/2), listput(list, (t-1)/2))), forprime(q = p, sqrtnint(B\m, n), my(t=m*q); list=concat(list, f(t, q, n-1)))); list); vecsort(Vec(f(1, 3, n)));
a(n) = my(x=2^n, y=2*x); while(1, my(v=generate(x, y, n)); if(#v >= 1, return(v[1])); x=y+1; y=2*x); \\ Daniel Suteu, Feb 05 2023
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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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