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A167874 The number of distinct primes < 10^n which are members of twin-prime pairs. 0
3, 15, 69, 409, 2447, 16337, 117959, 880623, 6849011, 54825357, 448752095, 3741170439, 31669329743, 271560643329, 2354418484607, 20608371394595, 181897678706317, 1617351777154871 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Number of terms in A001097 with at most n digits.

The entries are odd because 5 is counted only once, although it is a member of two twin prime pairs, (3,5) and (5,7).

Cardinality of the set of {A001359 U A006512} with entries < 10^n. - R. J. Mathar, Nov 23 2009

LINKS

Table of n, a(n) for n=1..18.

FORMULA

a(n) = 2*A007508(n) - 1.

EXAMPLE

There are exactly a(2) = 15 distinct primes below 10^2 that form twin primes (p, p+2), namely,

3, 5, 7, 11, 13, 17, 19, 29, 31, 41, 43, 59, 61, 71, 73 :

(3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), (71, 73).

CROSSREFS

Cf. A001097, A077800, A007508.

Sequence in context: A224749 A122558 A110211 * A318967 A277370 A213140

Adjacent sequences:  A167871 A167872 A167873 * A167875 A167876 A167877

KEYWORD

nonn

AUTHOR

Lekraj Beedassy, Nov 14 2009

EXTENSIONS

Definition rephrased by R. J. Mathar, Nov 23 2009

STATUS

approved

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Last modified January 20 23:20 EST 2019. Contains 319343 sequences. (Running on oeis4.)