cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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

This page as a plain text file.
%I A178755 #13 Apr 25 2015 12:00:16
%S A178755 44,46,49,64,66,69,94,96,99,104,155,215,221,222,225,226,251,255,262,
%T A178755 265,333,334,335,338,339,349,355,358,385,393,394,395,469,515,551,555,
%U A178755 557,558,577,585,587,622,625,655,695,774,777,822,825,826,855,857,862,865
%N A178755 Integers that become semiprime when any single digit is removed.
%C A178755 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, ....
%C A178755 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, ....
%C A178755 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, ....
%H A178755 Harvey P. Dale, <a href="/A178755/b178755.txt">Table of n, a(n) for n = 1..1000</a>
%F A178755 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.
%t A178755  Select[Range[3000],Union[PrimeOmega[FromDigits/@Subsets[IntegerDigits[#],{IntegerLength[#]-1}]]]=={2}&] (* _Harvey P. Dale_, Apr 25 2015 *)
%Y A178755 Cf. A001358, A034895, A107342.
%K A178755 base,nonn
%O A178755 1,1
%A A178755 _Jonathan Vos Post_, Jun 09 2010
%E A178755 Extended by _Ray Chandler_