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 A104646 Smallest semiprime equal to the sum of n distinct primes. 1
 9, 10, 21, 34, 51, 58, 77, 106, 129, 166, 201, 262, 287, 334, 381, 454, 501, 586, 669, 718, 791, 922, 989, 1082, 1167, 1282, 1371, 1486, 1623, 1754, 1851, 2018, 2127, 2326, 2427, 2638, 2747, 2974, 3093, 3274, 3459, 3694, 3831, 4034, 4227, 4534, 4661, 4894, 5123, 5366 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 COMMENTS The sequence is monotonic for its first million terms. Does there exist n with a(n) < a(n-1)? [Charles R Greathouse IV, Aug 24 2011] LINKS Charles R Greathouse IV, Table of n, a(n) for n = 2..10000 EXAMPLE a(2) = 9 because 9 = 2+7=9 = 3*3; a(3) = 10 because 10 = 2+3+5 = 2*5; a(4) = 21 because 21 = 2+3+5+11 = 3*7. PROG (PARI) issemi(n)=bigomega(n)==2 a(n)={ my(v=primes(n+3), s=sum(i=1, n+1, v[i]), m, t, t1); m=s+v[n+2]-5; forstep(i=n+1, 1, -1, t=s-v[i]; if(t >= m, break); if(issemi(t), return(t)) ); s+=v[n+2]; m=s+v[n+3]-10; for(i=2, n+2, t=s-v[i]; for(j=1, i-1, t1=t-v[j]; if(t1 >= m, break); if(issemi(t1), m=t1) ) ); if(issemi(m), return(m)); error("could not find a("n")") }; \\ Charles R Greathouse IV, Aug 24 2011 CROSSREFS Sequence in context: A178350 A085949 A102238 * A214425 A260184 A109463 Adjacent sequences: A104643 A104644 A104645 * A104647 A104648 A104649 KEYWORD nonn AUTHOR Giovanni Teofilatto, Apr 21 2005 EXTENSIONS a(6) corrected, a(7)-a(50) by Charles R Greathouse IV, Aug 24 2011 STATUS approved

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Last modified July 19 22:34 EDT 2024. Contains 374441 sequences. (Running on oeis4.)