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A188059 Numbers n with property that n, n+1 and n+(n+1) are all semiprimes. 1
25, 34, 38, 57, 93, 118, 133, 145, 177, 201, 205, 213, 218, 298, 334, 361, 381, 394, 446, 501, 633, 694, 698, 842, 865, 878, 898, 921, 1114, 1141, 1226, 1285, 1293, 1465, 1513, 1654, 1713, 1726, 1761, 1857, 1893, 1941, 1981, 2018, 2041, 2217, 2306, 2426, 2433, 2577, 2581, 2734, 2746, 2901, 2973, 3133, 3193, 3214, 3241, 3386, 3578, 3661, 3693, 3746, 3754, 3777, 3826, 3957 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Numbers n such that 2n+1 is a semiprime and sum of two consecutive semiprimes (n and n+1).

LINKS

Zak Seidov, Table of n, a(n) for n = 1..1309, a(n) up to 200000

FORMULA

A188059 = A111153 intersect A070552.  - M. F. Hasler, Mar 20 2011.

EXAMPLE

n=25=5*5, n+1=26=2*13, 2n+1=51=3*17.

MATHEMATICA

Select[Range[4000], Union[PrimeOmega[{#, #+1, 2 #+1}]]=={2}&] (* Harvey P. Dale, May 11 2012 *)

CROSSREFS

Cf. A001358 (semiprimes).

Cf. A176896 (safe semiprimes), A111153 (Sophie-Germain semiprimes), A070552.

Sequence in context: A020258 A227516 A281369 * A257720 A098368 A281370

Adjacent sequences:  A188056 A188057 A188058 * A188060 A188061 A188062

KEYWORD

nonn

AUTHOR

Zak Seidov, Mar 20 2011

STATUS

approved

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Last modified August 23 01:06 EDT 2019. Contains 326211 sequences. (Running on oeis4.)