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A174838 Numbers n such that semiprime(n)+1 is prime, where semiprime(n) is A001358. 1
1, 2, 4, 8, 16, 21, 27, 35, 55, 58, 76, 84, 111, 113, 120, 143, 147, 155, 176, 183, 218, 252, 258, 265, 294, 304, 348, 377, 383, 387, 403, 424, 435, 444, 464, 525, 548, 582, 585, 593, 600, 633, 690, 694, 732, 787, 803, 810, 827, 841, 846, 877, 892, 900, 971 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

N is in the sequence iff semiprime(n) is of the form 2p where p is a Sophie Germain prime (A005384).

LINKS

Table of n, a(n) for n=1..55.

EXAMPLE

a(1)=1 because semiprime(1)+1=5=prime, a(2)=2 because semiprime(2)+1=7=prime, a(3)=4 because semiprime(4)+1=11=prime.

CROSSREFS

Cf. A000040, A001358, A005384.

Sequence in context: A350414 A045776 A102252 * A308149 A196871 A334423

Adjacent sequences:  A174835 A174836 A174837 * A174839 A174840 A174841

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Mar 30 2010

EXTENSIONS

Edited, corrected and extended by Ray Chandler, Apr 05 2010

STATUS

approved

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Last modified August 16 21:38 EDT 2022. Contains 356169 sequences. (Running on oeis4.)