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 A133126 Semiprimes which are equal to product of two successive primes and also to sum of three successive primes. 1
 15, 143, 11021, 154433, 159197, 194477, 213443, 364807, 412163, 462391, 484391, 685583, 853751, 1032247, 1299479, 1633283, 2039183, 2108303, 2301253, 2985959, 3474487, 3802499, 3904567, 3960091, 4028033, 4536899, 5048993, 5517797 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS David A. Corneth, Table of n, a(n) for n = 1..10000 (first 350 terms form Harvey P. Dale) EXAMPLE 15 = 3*5 = 3 + 5 + 7, 143 = 11*13 = 43 + 47 + 53, 11021 = 103*107 = 3671 + 3673 + 3677, 154433 = 389*397 = 51473 + 51479 + 51481, 159197 = 397*401 = 53051 + 53069 + 53077, 194477 = 439*443 = 64811 + 64817 + 64849, 213443 = 461*463 = 71143 + 71147 + 71153. MATHEMATICA b = {}; For[n = 2, n < 1000, n++, a = Prime[n]*Prime[n + 1]; If[a == Prime[PrimePi[a/3]] + Prime[PrimePi[a/3] + 1] + Prime[PrimePi[a/3] + 2] || a == Prime[PrimePi[a/3] - 1] + Prime[PrimePi[a/3]] + Prime[PrimePi[a/3] + 1], AppendTo[b, a]]]; b (* Stefan Steinerberger, Sep 24 2007 *) stspQ[n_]:=Module[{ppi=PrimePi[n/3]}, MemberQ[Total/@Partition[ Prime[ Range[ ppi-10, ppi+10]], 3, 1], n]]; With[{nn=500}, Select[ Times@@@ Partition[ Prime[Range[nn]], 2, 1], stspQ]]//Quiet PROG (PARI) upto(n) = {res = List(); q = 2; forprime(p = 3, sqrtint(n), if(is(p*q), listput(res, p*q); print1(p*q", "); ); q = p; ); res } is(n) = { my(pp = precprime(n \ 3), np = nextprime(pp+1)); r = n - pp - np; if(r > np, return(r == nextprime(np + 1)) ); if(r < pp, return(r == precprime(pp - 1)) ); 0 } \\ David A. Corneth, Aug 22 2020 CROSSREFS Sequence in context: A173406 A291619 A071700 * A240158 A255944 A243418 Adjacent sequences: A133123 A133124 A133125 * A133127 A133128 A133129 KEYWORD nonn,easy AUTHOR Zak Seidov, Sep 19 2007 EXTENSIONS More terms from Stefan Steinerberger and R. J. Mathar, Sep 24 2007 STATUS approved

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Last modified March 30 07:38 EDT 2023. Contains 361606 sequences. (Running on oeis4.)