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 A034690 Sum of digits of all the divisors of n. 21
 1, 3, 4, 7, 6, 12, 8, 15, 13, 9, 3, 19, 5, 15, 15, 22, 9, 30, 11, 15, 14, 9, 6, 33, 13, 15, 22, 29, 12, 27, 5, 27, 12, 18, 21, 46, 11, 24, 20, 27, 6, 33, 8, 21, 33, 18, 12, 52, 21, 21, 18, 26, 9, 48, 18, 48, 26, 27, 15, 42, 8, 15, 32, 37, 21, 36, 14, 36, 24, 36, 9, 69, 11, 24, 34 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS First occurrence of k, or 0 if k never appears: 1, 0, 2, 3, 13, 5, 4, 7, 10, 0, 19, 6, 9, 21, 8, 403, 79, 34, 12, 39, 35, 16, 129, 38, 133, 52, 30, 100, 28, 18, 81, 63, 24, 75, 333, 66, 64, 117, 99, 243, ..., . - Robert G. Wilson v, Oct 25 2006 Numbers k for which there is no a(): {2, 10} with 1834 being the first one in question. - Robert G. Wilson v, Oct 25 2006 The only fixed points are 1 and 15. These are also the only loops of iterations of A034690: see the SeqFan thread "List the divisors...". - M. F. Hasler, Nov 08 2015 The following sequence is composed of numbers n such that the sum of digits of all divisors of n equals 15: 8, 14, 15, 20, 26, 59, 62, ... It actually depicts the positions of number 15 in this sequence: see the SeqFan thread "List the divisors...". - V.J. Pohjola, Nov 09 2015 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 H. Havermann et al, in reply to E. Angelini, List the dividers, sum the digits, SeqFan list, Nov. 2015. Maxwell Schneider, Robert Schneider, Digit sums and generating functions, arXiv:1807.06710 [math.NT], 2018. See (22) p. 6. EXAMPLE a(15) = 1 + 3 + 5 + (1+5) = 15. - M. F. Hasler, Nov 08 2015 MAPLE with(numtheory); read transforms; f:=proc(n) local t1, t2, i; t1:=divisors(n); t2:=0; for i from 1 to nops(t1) do t2:=t2+digsum(t1[i]); od: t2; end; # Alternative: sd:= proc(n) option remember; local k; k:= n mod 10; k + procname((n-k)/10) end proc: for n from 0 to 9 do sd(n):= n od: a:= n -> add(sd(d), d=numtheory:-divisors(n)): map(a, [\$1..100]); # Robert Israel, Nov 17 2015 MATHEMATICA Table[Plus @@ Flatten@ IntegerDigits@ Divisors@n, {n, 75}] (* Robert G. Wilson v, Sep 30 2006 *) PROG (Haskell) a034690 = sum . map a007953 . a027750_row -- Reinhard Zumkeller, Jan 20 2014 (PARI) vector(100, n, sumdiv(n, d, sumdigits(d))) \\ Michel Marcus, Jun 28 2015 (PARI) A034690(n)=sumdiv(n, d, sumdigits(d)) \\ For use in other sequences. - M. F. Hasler, Nov 08 2015 CROSSREFS Cf. A000005, A000203, A007953, A086793. Cf. A093653 (Binary equivalent.) Sequence in context: A088000 A284344 A168338 * A069192 A076887 A140782 Adjacent sequences:  A034687 A034688 A034689 * A034691 A034692 A034693 KEYWORD base,easy,nonn AUTHOR STATUS approved

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Last modified April 13 03:43 EDT 2021. Contains 342934 sequences. (Running on oeis4.)