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 A339652 a(n) is the least number k such that 2*k+1 has exactly n expressions as p+2*q where p and q are primes, or 0 if there is no such k. 1
 1, 3, 4, 10, 8, 16, 22, 25, 37, 49, 55, 46, 52, 67, 76, 100, 82, 124, 115, 118, 160, 112, 136, 181, 205, 196, 142, 157, 235, 241, 217, 202, 232, 277, 340, 247, 391, 337, 436, 424, 481, 864, 292, 262, 448, 397, 520, 457, 367, 427, 595, 412, 382, 547, 487, 502, 517, 562, 655, 703, 598, 760, 592 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Conjecture: all a(n) > 0. LINKS Robert Israel, Table of n, a(n) for n = 0..9400 FORMULA A046927(a(n)) = n if a(n) > 0. EXAMPLE a(4) = 8 because 2*8+1 = 17 has exactly 4 representations as p+2*q: 17 = 3 + 2*7 = 7 + 2*5 = 11 + 2*3 = 13 + 2*2, and this is not true for any k < 8. MAPLE # given table A046927 R:= Array(0..100): for i from 0 to max(indices(A046927)) do v:= A046927[i]; if R[v]= 0 then R[v]:= i fi od: seq(R[i], i=0..100); PROG (PARI) f(n) = my(s); n=2*n+1; forprime(p=2, n\2, s+=isprime(n-2*p)); s; a(n) = my(k=1); while(f(k) != n, k++); k; \\ Michel Marcus, Dec 14 2020 CROSSREFS Cf. A046927, A339709. Sequence in context: A343876 A356150 A222136 * A279787 A128488 A359366 Adjacent sequences: A339649 A339650 A339651 * A339653 A339654 A339655 KEYWORD nonn AUTHOR J. M. Bergot and Robert Israel, Dec 13 2020 STATUS approved

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Last modified August 6 00:15 EDT 2024. Contains 374957 sequences. (Running on oeis4.)