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 A371808 Exponents k > 0 of powers of 2 such that the decimal expansion of 2^k contains more than one 666 substring (overlapping substrings are counted as distinct). 4
 220, 222, 243, 529, 624, 648, 662, 702, 714, 838, 840, 842, 844, 846, 850, 857, 859, 867, 869, 871, 924, 925, 927, 929, 931, 975, 979, 981, 983, 1056, 1058, 1062, 1088, 1133, 1135, 1160, 1162, 1219, 1230, 1241, 1259, 1310, 1341, 1343, 1349, 1384, 1394, 1411, 1420 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS A positive power of 2 containing 666 in its decimal expansion is called an apocalyptic number. See A371806 for a variant counting only nonoverlapping substrings. LINKS Paolo Xausa, Table of n, a(n) for n = 1..10000 Brady Haran and Tony Padilla, Apocalyptic Numbers, YouTube Numberphile video, 2024. Eric Weisstein's World of Mathematics, Apocalyptic Number. EXAMPLE 243 is a term because 2^243 contains two (overlapping) 666 substrings in its decimal expansion: . *** 14134776518227074636666380005943348126619871175004951664972849610340958208. *** MATHEMATICA Select[Range[2000], StringCount[IntegerString[2^#], "666", Overlaps->True] > 1 &] PROG (Python) def ok(n): return (s:=str(1< 1 or "6666" in s print([k for k in range(2000) if ok(k)]) # Michael S. Branicky, Apr 07 2024 CROSSREFS Subsequence of A007356. Cf. A371806, A371809. Sequence in context: A157645 A157673 A064477 * A371806 A217160 A203777 Adjacent sequences: A371805 A371806 A371807 * A371809 A371810 A371811 KEYWORD nonn,easy,base AUTHOR Paolo Xausa, Apr 06 2024 STATUS approved

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Last modified September 12 11:23 EDT 2024. Contains 375850 sequences. (Running on oeis4.)