A242102 - OEIS

A242102

Semiprimes that are the concatenation of a prime and the previous prime.

1713, 2319, 2923, 4341, 6159, 7167, 8983, 103101, 151149, 157151, 163157, 167163, 173167, 191181, 197193, 233229, 257251, 277271, 283281, 311307, 337331, 367359, 373367, 421419, 431421, 439433, 449443, 463461, 467463, 479467, 487479, 509503, 521509, 547541, 557547

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OFFSET

1,1

LINKS

K. D. Bajpai, Table of n, a(n) for n = 1..11480

EXAMPLE

13 and 17 are consecutive primes. Their reverse concatenation = 1713 = 3 * 571, which is semiprime.

19 and 23 are consecutive primes. Their reverse concatenation = 2319 = 3 * 773, which is semiprime.

MAPLE

select(k -> numtheory:-bigomega(k)=2, [seq(parse(cat(ithprime(n+1), ithprime(n))), n=1..200)]);

MATHEMATICA

A242102 = {}; Do[t = FromDigits[Flatten[IntegerDigits /@ {Prime[n], Prime[n - 1]}]]; If[PrimeOmega[t] == 2, AppendTo[A242102, t]], {n, 2, 200}]; A242102

PROG

(PARI)

forprime(p=1, 10^3, q=concat(Str(p), Str(precprime(p-1))); if(bigomega(eval(q))==2, print1(eval(q), ", "))) \\ Derek Orr, Aug 15 2014

CROSSREFS

Cf. A000040, A001358, A007796, A088784.

Sequence in context: A293480 A227218 A280113 * A221481 A008744 A184090

Adjacent sequences: A242099 A242100 A242101 * A242103 A242104 A242105

KEYWORD

nonn,base

AUTHOR

K. D. Bajpai, Aug 15 2014

STATUS

approved