A178755 Integers that become semiprime when any single digit is removed.

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

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: A225619 A121610 A254752 * A182261 A061757 A342187

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