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 A344422 Palindromes having more divisors than all smaller palindromes. 5
 1, 2, 4, 6, 44, 66, 252, 2112, 2772, 6336, 27972, 48384, 219912, 252252, 696696, 828828, 2114112, 4228224, 21333312, 42666624, 63999936, 234666432, 2154664512, 2329559232, 4815995184, 8402442048, 21354645312, 40362626304, 63708380736, 211887788112 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A000005(a(n)) = 1, 2, 3, 4, 6, 8, 18, 28, 36, 42, 48, 72, 96, 108, 128, 144, 168, 192, 336, 384, .... - Felix Fröhlich, May 19 2021 From Jon E. Schoenfield, Jun 22 2021: (Start) There exists at least one m-digit term for every m in 1..22 except 21 (see the b-file). Conjecture: all terms after a(1)=1 are even. (End) LINKS Jon E. Schoenfield, Table of n, a(n) for n = 1..59 (all terms < 10^22) David A. Corneth, PARI program Jon E. Schoenfield, C# program FORMULA A000005(a(n)) = A345250(n). EXAMPLE Terms include: 4 (3 divisors); 6 (4 divisors); 44 (6 divisors); 66 (8 divisors); 252 (18 divisors). MATHEMATICA pal=Union@Flatten[Table[r=IntegerDigits@n; FromDigits/@(Join[r, #]&/@{Reverse@r, Rest@Reverse@r}), {n, 10^5}]]; m=0; lst={}; Do[s=DivisorSigma[0, k]; If[s>m, AppendTo[lst, k]; m=s], {k, pal}]; lst (* Giorgos Kalogeropoulos, Dec 08 2021 *) PROG (C#) See C# link // Jon E. Schoenfield, Jun 19 2021 (PARI) See PARI link \\ David A. Corneth, May 18 2021 CROSSREFS Cf. A000005, A002113 (palindromes), A076888 (their number of divisors), A002182, A084324, A093036, A345250. Sequence in context: A173818 A263541 A283157 * A084324 A329529 A333456 Adjacent sequences: A344419 A344420 A344421 * A344423 A344424 A344425 KEYWORD nonn,base AUTHOR Bhupendra Kumar Singh, May 17 2021 EXTENSIONS Data corrected and extended by David A. Corneth, May 18 2021 STATUS approved

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Last modified April 20 21:11 EDT 2024. Contains 371845 sequences. (Running on oeis4.)