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A244057 Semiprimes which are concatenation of two consecutive primes. 2
35, 57, 1317, 1923, 2329, 2931, 4143, 5359, 5961, 6167, 7379, 8997, 103107, 131137, 181191, 193197, 211223, 227229, 281283, 307311, 347349, 367373, 379383, 383389, 421431, 443449, 503509, 547557, 557563, 577587, 587593, 593599, 607613, 619631, 641643, 691701, 709719 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The semiprimes in A045533.

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..10000

Index entries for sequences related to decimal expansion of n

Index entries for sequences related to semiprimes

EXAMPLE

35 is in the sequence because the concatenation of [3, 5] = 35 = 5 * 7, which is semiprime.

1923 is in the sequence because concatenation of [19, 23] = 1923 = 3 * 641, which is semiprime.

1113 is not in the sequence because, though 1113 is concatenation of two consecutive primes [11, 13], 1113 = 3 * 7 * 53, which is not semiprime.

MAPLE

with(numtheory):with(StringTools):A244057:= proc() local a, b, k; a:=ithprime(n); b:=ithprime(n+1); k:=parse(cat(a, b)); if bigomega(k)=2 then RETURN (k); fi; end: seq(A244057 (), n=1..200);

MATHEMATICA

A244057 = {}; Do[t = FromDigits[Flatten[IntegerDigits /@ {Prime[n], Prime[n + 1]}]]; If [PrimeOmega[t] == 2, AppendTo[A244057, t]], {n, 100}]; A244057

CROSSREFS

Cf. A000040, A001358, A030469, A045533, A244007.

Sequence in context: A267738 A219806 A095958 * A219457 A026064 A250764

Adjacent sequences:  A244054 A244055 A244056 * A244058 A244059 A244060

KEYWORD

nonn,base

AUTHOR

K. D. Bajpai, Jun 18 2014

STATUS

approved

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Last modified April 3 00:35 EDT 2020. Contains 333195 sequences. (Running on oeis4.)