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A232847
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Numbers n such that sum of divisors of n is a square and a triangular number (A000217). That is, numbers n such that A000203(n) is in A001110.
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2
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1, 22, 17310, 20802, 23110, 24262, 25995, 26542, 29427, 31735, 33835, 38137, 39287, 39859, 40967, 13595040, 14285160, 15129504, 15378336, 15834528, 15912936, 16327008, 16555752, 16897896, 16908264, 17054388, 17145432, 17749044, 18013428, 20239146, 20713482, 21265578
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OFFSET
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1,2
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LINKS
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EXAMPLE
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Sigma(22)=36. Because 36 is both a square and a triangular number, 22 is in the sequence.
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PROG
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(define A232847 (MATCHING-POS 1 1 (lambda (n) (inA001110? (A000203 n)))))
(define (inA001110? n) (and (zero? (A068527 n)) (inA001109? (floor->exact (sqrt n)))))
(define (inA001109? n) (= (* 8 n n) (floor->exact (* (sqrt 8) n (ceiling->exact (* (sqrt 8) n)))))) ;; Note: this is based on Benoit Cloitre's, May 10 2003 comment in A001109.
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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