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 A176651 Numbers k such that both semiprime(k)/prime(j+1) and semiprime(k+1)/prime(j) are prime for some j. 0
 3, 5, 6, 7, 10, 11, 15, 19, 20, 23, 24, 32, 46, 57, 63, 65, 69, 77, 85, 86, 98, 99, 108, 119, 123, 127, 130, 131, 132, 140, 150, 154, 161, 166, 167, 193, 205, 217, 233, 237, 264, 276, 280, 303, 307, 326, 331, 332, 339, 343, 362, 368, 369, 380, 382, 385, 386, 415 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Table of n, a(n) for n=1..58. EXAMPLE 3 is a term because semiprime(3)/prime(1+1) = 6/3 = 2 (prime) and semiprime(3+1)/prime(1) = 10/2 = 5 (prime); 5 is a term because semiprime(5)/prime(3+1) = 14/7 = 2 (prime) and semiprime(5+1)/prime(3) = 15/5 = 3 (prime). MAPLE isA176651 := proc(n) pfsn := convert(numtheory[factorset]( A001358(n) ), list) ; pfsn1 := convert(numtheory[factorset]( A001358(n+1) ), list) ; op(1, pfsn) = nextprime( op(1, pfsn1)) or op(1, pfsn) = nextprime( op(-1, pfsn1)) or op(-1, pfsn) = nextprime( op(1, pfsn1)) or op(-1, pfsn) = nextprime( op(-1, pfsn1)) ; end proc: for n from 1 to 600 do if isA176651(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, Apr 26 2010 CROSSREFS Sequence in context: A157201 A067351 A067350 * A359879 A028762 A047328 Adjacent sequences: A176648 A176649 A176650 * A176652 A176653 A176654 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Apr 22 2010 EXTENSIONS Corrected (6 inserted) and extended beyond 132 by R. J. Mathar, Apr 26 2010 STATUS approved

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Last modified September 30 02:05 EDT 2023. Contains 365781 sequences. (Running on oeis4.)