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 A269308 Consider a number x. Take the sum of its digits. Repeat the process deleting the first addendum and adding the previous sum. The sequence lists the numbers that after some iterations reach the sum of the divisors of x. 5
 20, 25, 43, 44, 49, 59, 122, 206, 2485, 11899, 17608, 24141, 56207, 195236, 2424613, 2842925, 6241233, 59087970, 111205290, 124735931, 224269761, 1086241193 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS 44 works in both directions: n -> sigma(n) and sigma(n) -> n. See A269307. LINKS EXAMPLE sigma(20) = 42 :  2 + 0 = 2; 0 + 2 = 2; 2 + 2 = 4; 2 + 4 = 6; 4 + 6 = 10; 6 + 10 = 16; 10 + 16 = 26; 16 +26 = 42. MAPLE with(numtheory): P:=proc(q, h) local a, b, k, n, t, v; v:=array(1..h); for n from 2 to q do a:=n; b:=ilog10(a)+1; if b>1 then for k from 1 to b do v[b-k+1]:=(a mod 10); a:=trunc(a/10); od; t:=b+1; v[t]:=add(v[k], k=1..b); while v[t]

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Last modified January 24 23:49 EST 2021. Contains 340414 sequences. (Running on oeis4.)