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 A308365 Numbers which are products of repunits. 4
 1, 11, 111, 121, 1111, 1221, 1331, 11111, 12221, 12321, 13431, 14641, 111111, 122221, 123321, 134431, 135531, 147741, 161051, 1111111, 1222221, 1233321, 1234321, 1344431, 1356531, 1367631, 1478741, 1490841, 1625151, 1771561, 11111111, 12222221, 12333321 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The number of terms below 10^n is A216053(n)-1 for 1 <= n <= 25, but not for larger n. - Rémy Sigrist, May 28 2019 The product of repunits is not necessarily palindromic, see A339676. - Bernard Schott, Apr 02 2021 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE a(11) = 13431 is in the sequence since it is the product of repunits (11^2*111). MAPLE d:= 10: # for terms < 10^d N:= 10^d: S:= {1}: for m from 2 to d do r:= (10^m-1)/9; k:= floor(log[r](N)); V:= S; for i from 1 to k do V:= select(`<`, map(`*`, V, r), N); S:= S union V od; od: sort(convert(S, list)); # Robert Israel, Nov 26 2020 CROSSREFS Cf. A002275 (repunits), A083278 (repunit powers), A216053, A339676 (nonpalindromic terms). Sequence in context: A358441 A135464 A231872 * A083278 A039987 A039989 Adjacent sequences: A308362 A308363 A308364 * A308366 A308367 A308368 KEYWORD nonn,base AUTHOR Sergio Pimentel, May 22 2019 EXTENSIONS Missing a(25) = 1356531 inserted by Ilya Gutkovskiy, Apr 14 2020 STATUS approved

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Last modified December 7 05:18 EST 2023. Contains 367629 sequences. (Running on oeis4.)