A108183 Primes equal to the sum of two successive semiprimes.
19, 29, 43, 47, 59, 67, 73, 127, 151, 167, 173, 233, 283, 313, 317, 461, 521, 541, 593, 653, 701, 719, 727, 787, 839, 907, 967, 1249, 1409, 1439, 1471, 1549, 1601, 1831, 1867, 1873, 1913, 1993, 2029, 2083, 2089, 2287, 2311, 2351, 2393, 2579, 2593, 2693
Offset: 1
Examples
19 = sp(3) + sp(4) = 9 + 10 where sp(n) = n-th semiprime. 29 is a member because 2*7 + 3*5 = 29. 13 is not a member because although 2*2 + 3*3 = 13, 4 and 9 are not successive semiprimes.
Links
- Zak Seidov, Table of n, a(n) for n = 1..10000
Crossrefs
Cf. A109404.
Programs
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Mathematica
Select[ Plus @@@ Partition[ Select[ Range[1250], Plus @@ Last /@ FactorInteger[ # ] == 2 &], 2, 1], PrimeQ[ # ] &] (* Robert G. Wilson v, Jun 14 2005 *) Select[Total/@Partition[Select[Range[1500],PrimeOmega[#]==2&],2,1], PrimeQ] (* Harvey P. Dale, Nov 15 2013 *)
Extensions
Corrected and extended by Robert G. Wilson v, Jun 14 2005
Edited by N. J. A. Sloane, May 03 2007
Comments