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A178755 Integers that become semiprime when any single digit is removed. 1
44, 46, 49, 64, 66, 69, 94, 96, 99, 104, 155, 215, 221, 222, 225, 226, 251, 255, 262, 265, 333, 334, 335, 338, 339, 349, 355, 358, 385, 393, 394, 395, 469, 515, 551, 555, 557, 558, 577, 585, 587, 622, 625, 655, 695, 774, 777, 822, 825, 826, 855, 857, 862, 865 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The subsequence of semiprimes begins: 46, 49, 69, 94, 155, 215, 221, 226, 262, 265, 334, 335, 339, 355, 358, 393, 394, 395, 469, 515, 551, 622, 655, 695, 862, 865, 914, 933, 934, 951, 955, 1111, 1115, 1119, 1159, 1219, 1411, 1415, 1466, 2021, 2026, 2062, 2095, 2159, 2899, 2959, 2995, 2998, 3035, 3039, ....

The subsequence of primes begins: 251, 349, 557, 577, 587, 857, 877, 1559, 1669, 4111, 4973, 5051, 5119, 5519, 5591, 6299, 6679, 6871, 6899, 6949, 7213, 7789, 7949, 7993, 8669, 8699, 9133, 9221, 9551, 9749, ....

This is to semiprimes A001358 as A034895 is to primes A000040. Note that this is not a subset of A107342, as there are values with nonsemiprime digits, beginning with 104, 155, 215, 221, 222, ....

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(10) = 104 because deleting the "1" gives "04" which by OEIS protocol becomes the semiprime 4=2*2; deleting the "0" gives the semiprime 14=2*7; and deleting the "4" gives the semiprime 10=2*5.

MATHEMATICA

Select[Range[3000], Union[PrimeOmega[FromDigits/@Subsets[IntegerDigits[#], {IntegerLength[#]-1}]]]=={2}&] (* Harvey P. Dale, Apr 25 2015 *)

CROSSREFS

Cf. A001358, A034895, A107342.

Sequence in context: A121610 A254752 A063837 * A182261 A061757 A088066

Adjacent sequences:  A178752 A178753 A178754 * A178756 A178757 A178758

KEYWORD

base,nonn

AUTHOR

Jonathan Vos Post, Jun 09 2010

EXTENSIONS

Extended by Ray Chandler

STATUS

approved

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Last modified July 14 16:21 EDT 2020. Contains 335729 sequences. (Running on oeis4.)