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.
%I A280383 #10 Jul 12 2023 11:20:25 %S A280383 4,6,12,18,19,30,34,42,51,55,56,60,72,86,92,94,102,108,138,142,144, %T A280383 150,160,180,184,186,192,198,202,204,214,216,218,220,228,236,240,243, %U A280383 248,249,266,270,282,300,302,304,307,312,320,322,328,340,341,348,349,392,394,412,414,416,420,424,432,446,452,462,470,472,476,491,516,518,522,534,536,544,552,570,580,582,590,600,604,618,634,638,642,660,664,668,670,680,686,688,696,698,701,722 %N A280383 Numbers n such that n-1 has the same count of prime factors as n+1 when including multiplicity and also when not. %C A280383 First differs from its subsequence A074997 at a(97) = 701 because A074997(97) = 722. %H A280383 Rick L. Shepherd, <a href="/A280383/b280383.txt">Table of n, a(n) for n = 1..10000</a> %F A280383 Sequence is A088070 INTERSECT A280382. %e A280383 The number 19 is a term because 18 = 2*3^2 and 20 = 2^2*5 each have two distinct prime factors and each have three prime factors when counted with multiplicity. %t A280383 Select[Range[800],PrimeNu[#]==PrimeNu[#+2]&&PrimeOmega[#]==PrimeOmega[#+2]&]+1 (* _Harvey P. Dale_, Jul 12 2023 *) %o A280383 (PARI) IsInA280383(n) = n > 1 && bigomega(n-1) == bigomega(n+1) && omega(n-1) == omega(n+1) %Y A280383 Cf. A001221, A001222, A074997, A088070, A280382. %K A280383 nonn %O A280383 1,1 %A A280383 _Rick L. Shepherd_, Jan 02 2017