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 A362003 #30 Apr 23 2023 22:43:52 %S A362003 42,66,78,362,1086,1122,1254,1794,1810,1846,1974,2534,2730,3318,3982, %T A362003 4890,5538,5590,6006,6214,9230,12922,12990,13515,15510,16205,17430, %U A362003 18642,20306,22170,23170,25098,26962,27030,29274,31070,32142,32410 %N A362003 Squarefree composite numbers m such that k - m^2 < m, where k is the smallest number greater than m^2 such that rad(k) | m. %C A362003 Most small squarefree m have k - m^2 > m. For prime m = p, k = p^3, hence (p^3 - p^2) > p. %F A362003 This sequence is { m : A362045(n) - m^2 < m and m in A120944 }. %e A362003 a(1) = 42 since 42 is the smallest squarefree number such that the smallest k > m^2 such that rad(k) | m also has difference k - m^2 < m. %e A362003 Table showing a(n) = A120944(i) = m, A362045(i) = k, and the difference k-m^2. %e A362003 i m k (k-m^2) %e A362003 ----------------------------- %e A362003 14 42 1792 28 %e A362003 22 66 4374 18 %e A362003 27 78 6144 60 %e A362003 147 362 131072 28 %e A362003 478 1086 1179648 252 %e A362003 495 1122 1259712 828 %e A362003 558 1254 1572864 348 %e A362003 813 1794 3219264 828 %e A362003 822 1810 3276800 700 %e A362003 840 1846 3407872 156 %e A362003 900 1974 3898368 1692 %t A362003 s = Select[Range[6, 400], And[CompositeQ[#], SquareFreeQ[#]] &]; Reap[Do[(m = #^2 + 1; While[! Divisible[#, Times @@ FactorInteger[m][[All, 1]]], m++]; If[m - #^2 < #, Sow[#]]) &[s[[i]]], {i, Length[s]}] ][[-1, -1]] %o A362003 (PARI) rad(n) = factorback(factorint(n)[, 1]); \\ A007947 %o A362003 isok(m) = if (!isprime(m) && issquarefree(m), for (k=1+m^2, m+m^2, if (!(m % rad(k)), return(1)))); \\ _Michel Marcus_, Apr 21 2023 %Y A362003 Cf. A007947, A120944, A362045. %K A362003 nonn %O A362003 1,1 %A A362003 _Michael De Vlieger_, Apr 05 2023