This site is supported by donations to The OEIS Foundation. Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A054973 Number of numbers whose divisors sum to n. 34
 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 2, 1, 1, 1, 0, 0, 2, 0, 1, 0, 0, 0, 3, 0, 0, 0, 1, 0, 1, 2, 2, 0, 0, 0, 1, 0, 1, 1, 1, 0, 3, 0, 1, 0, 0, 0, 3, 0, 0, 0, 0, 0, 2, 0, 2, 1, 0, 0, 3, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 5, 0, 1, 0, 0, 0, 1, 0, 2, 0, 0, 0, 3, 0, 0, 0, 0, 0, 3, 1, 0, 1, 0, 0, 4, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,12 COMMENTS a(n) = frequency of values n in A000203(m), where A000203(m) = sum of divisors of m. a(n) >= 1 for such n that A175192(n) = 1, a(n) >= 1 if A000203(m) = n for any m. a(n) = 0 for such n that A175192(n) = 0, a(n) = 0 if A000203(m) = n has no solution. - Jaroslav Krizek, Mar 01 2010 First occurrence of k: 2, 1, 12, 24, 96, 72, ..., = A007368. - Robert G. Wilson v, May 14 2014 a(n) is also the number of positive terms in the n-th row of triangle A299762. - Omar E. Pol, Mar 14 2018 LINKS T. D. Noe, Table of n, a(n) for n = 1..10000 EXAMPLE a(12)=2 since 11 has factors 1 and 11 with 1+11=12 and 6 has factors 1, 2, 3 and 6 with 1+2+3+6=12. MATHEMATICA nn = 105; t = Table[0, {nn}]; k = 1; While[k < 6 nn^(3/2)/Pi^2, d = DivisorSigma[1, k]; If[d < nn + 1, t[[d]]++]; k++]; t (* Robert G. Wilson v, May 14 2014 *) PROG (PARI) a(n)=v = vector(0); for (i = 1, n, if (sigma(i) == n, v = concat(v, i)); ); #v; \\ Michel Marcus, Oct 22 2013 (PARI) a(n)=sum(k=1, n, sigma(k)==n) \\ Charles R Greathouse IV, Nov 12 2013 (PARI) first(n)=my(v=vector(n), t); for(k=1, n, t=sigma(n); if(t<=n, v[t]++)); v \\ Charles R Greathouse IV, Mar 08 2017 CROSSREFS An inverse to the sum-of-divisors function A000203, For partial sums see A074753. Cf. A002191, A007609. Sequence in context: A089053 A214979 A068462 * A030351 A257994 A188921 Adjacent sequences:  A054970 A054971 A054972 * A054974 A054975 A054976 KEYWORD nonn AUTHOR Henry Bottomley, May 16 2000 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified September 20 16:48 EDT 2019. Contains 327242 sequences. (Running on oeis4.)