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A204541 Semiprimes with semiprime "look and say" descriptions. 1
4, 14, 15, 21, 22, 35, 38, 55, 57, 74, 87, 95, 119, 143, 145, 166, 187, 205, 215, 217, 247, 253, 254, 259, 278, 287, 289, 291, 305, 314, 335, 339, 341, 394, 403, 407, 427, 471, 493, 505, 514, 515, 517, 538, 553, 559, 565, 589, 614, 622, 623, 629, 633, 634, 649 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Semiprime analogous to A056815.

LINKS

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

EXAMPLE

14 is in the sequence because 14 is a semiprime (2*7) and its "Look and Say", 1114 is also a semiprime (2*557).

MATHEMATICA

LookAndSayA[n_] := FromDigits@ Flatten@ IntegerDigits@ Flatten[ Through[ {Length, First}[#]] & /@ Split@ IntegerDigits@ n]; semiPrimeQ[n_] := Plus @@ Last /@ FactorInteger@ n == 2; Select[ Range@ 650, semiPrimeQ@# && semiPrimeQ@ LookAndSayA@# &]

CROSSREFS

Cf. A001358, A056815.

Sequence in context: A229392 A229320 A127302 * A020157 A101237 A180333

Adjacent sequences:  A204538 A204539 A204540 * A204542 A204543 A204544

KEYWORD

easy,nonn

AUTHOR

Robert G. Wilson v, Jan 27 2012

STATUS

approved

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Last modified November 29 17:50 EST 2021. Contains 349416 sequences. (Running on oeis4.)