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 A226930 Second differences give the sequence itself, but read digit-by-digit. 2
 1, 2, 4, 8, 16, 32, 49, 72, 98, 126, 158, 199, 247, 297, 356, 423, 491, 561, 637, 714, 796, 886, 977, 1077, 1186, 1297, 1412, 1534, 1658, 1791, 1931, 2074, 2222, 2376, 2534, 2694, 2857, 3024, 3200, 3377, 3559, 3747, 3936 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS There are many sequences with this property, but this is the lexicographically earliest such sequence which has positive terms and is strictly increasing. For a discussion of the growth rate, see A227844. - N. J. A. Sloane, Aug 20 2013 LINKS Alois P. Heinz and N. J. A. Sloane, Table of n, a(n) for n = 1..20000 EXAMPLE The second differences are 1, 2, 4, 8, 1, 6, 3, 2, 4, 9, 7, 2, 9, 8, 1, 2, 6, 1, 5, 8, 1, 9, 9, 2, 4, 7, ... MAPLE # From N. J. A. Sloane, Aug 21 2013 a:=[1, 2, 4]; b:=[1, 2]; c:=[1]; la:=3; lb:=2; lc:=1; M:=100; p:=2; for n from 1 to M do N:=a[p]; s:=convert(N, base, 10); ls:=nops(s); for i from 1 to ls do c:=[op(c), s[ls-i+1]]; lc:=lc+1; b:=[op(b), b[lb]+c[lc]]; lb:=lb+1; a:=[op(a), a[la]+b[lb]]; la:=la+1;                    od: p:=p+1; od: [seq(a[i], i=1..la)]; PROG Haskell program from Arie Groeneveld, Aug 31 2013: digits = map (fromIntegral.digitToInt). show inverseDiff xs = scanl (+) (head xs) xs seqA = iterate ((!!2). iterate inverseDiff. concatMap digits) [1] Example (executed in GHCi): > seqA !!4 [1, 2, 4, 8, 16, 32, 49, 72, 98, 126, 158, 199, 247, 297] CROSSREFS Cf. A227844. Sequence in context: A326079 A222193 A217833 * A297702 A306314 A007055 Adjacent sequences:  A226927 A226928 A226929 * A226931 A226932 A226933 KEYWORD nonn,base AUTHOR Eric Angelini, Jul 30 2013 EXTENSIONS More terms from Paolo P. Lava, Jul 30 2013 STATUS approved

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Last modified June 24 17:58 EDT 2019. Contains 324330 sequences. (Running on oeis4.)