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 A117948 Sum of the divisors of pentagonal numbers. 3
 1, 6, 28, 36, 48, 72, 144, 168, 182, 180, 372, 576, 280, 336, 864, 720, 558, 702, 1120, 1080, 1024, 1008, 1296, 2016, 1178, 1344, 3600, 2016, 1320, 2160, 2304, 3720, 2736, 1836, 4704, 4212, 2736, 2280, 5040, 6048, 2604, 4992, 5588, 4752, 5304, 3312 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS See also: A000326 Pentagonal numbers: n(3n-1)/2. A000203 sigma(n) = sum of divisors of n. Also called sigma_1(n). A074285 Sum of the divisors of n-th triangular number. A117949 Indices of pentagonal numbers whose sum of divisors is square. LINKS Amiram Eldar, Table of n, a(n) for n = 1..10000 FORMULA a(n) = sigma(n(3n-1)/2), where sigma is the sum of divisors function. - Emeric Deutsch, Apr 15 2006 EXAMPLE a(5)=48 because the divisors of 5*(3*5-1)/2=35 are 1,5,7 and 35, having sum 48. MAPLE with(numtheory): seq(sigma(n*(3*n-1)/2), n=1..46); # Emeric Deutsch, Apr 15 2006 MATHEMATICA Table[DivisorSigma[1, (n(3n-1))/2], {n, 50}] (* Harvey P. Dale, Jul 05 2015 *) CROSSREFS Cf. A000203, A000326, A074285, A117949. Sequence in context: A083865 A185351 A272971 * A252234 A242344 A247111 Adjacent sequences:  A117945 A117946 A117947 * A117949 A117950 A117951 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, Apr 04 2006 EXTENSIONS a(0) removed by Amiram Eldar, Aug 17 2019 STATUS approved

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Last modified October 14 07:00 EDT 2019. Contains 327995 sequences. (Running on oeis4.)