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A083681 Sum of divisors of semiprimes. 4
7, 12, 13, 18, 24, 24, 32, 36, 31, 42, 48, 54, 48, 60, 56, 72, 57, 72, 72, 80, 90, 96, 84, 96, 114, 96, 126, 108, 132, 120, 112, 128, 144, 120, 162, 152, 144, 180, 144, 133, 186, 168, 176, 160, 204, 192, 216, 168, 180, 222, 192, 240, 216, 192, 252, 183, 240, 270, 248 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Contains all products of distinct terms of A008864 contributed by the squarefree semiprimes and all terms of A060800 contributed by the squared primes: 7 = A060800(1), 12 = A008864(1)*A008864(2), 13 = A060800(2), 18=A008864(1)*A008864(3) etc. - R. J. Mathar, Mar 15 2018

LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = A000203(A001358(n)) = 1 + A020639(n) + A057427(A006530(n)-A020639(n))*A006530(n) + A020639(n)*A006530(n). - Reinhard Zumkeller, Jun 16 2003

EXAMPLE

a(2) = 12 because the sum of divisors of the 2nd semiprime, i.e. 6, is 1+2+3+6 = 12.

MATHEMATICA

DivisorSigma[1, Select[Range[200], PrimeOmega[#] == 2 &]] (* Amiram Eldar, Nov 24 2020 *)

CROSSREFS

Cf. A000203, A001358, A006530, A008864, A020639, A060800.

Sequence in context: A223423 A274334 A328414 * A178660 A048653 A205807

Adjacent sequences:  A083678 A083679 A083680 * A083682 A083683 A083684

KEYWORD

easy,nonn

AUTHOR

Shyam Sunder Gupta, Jun 15 2003

STATUS

approved

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Last modified July 29 05:20 EDT 2021. Contains 346340 sequences. (Running on oeis4.)