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A232847 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. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Donovan Johnson, Table of n, a(n) for n = 1..136 (terms with sigma values <= A001110(8))

EXAMPLE

Sigma(22)=36. Because 36 is both a square and a triangular number, 22 is in the sequence.

PROG

(Scheme, with Antti Karttunen's IntSeq-library)

(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.

;; Note: Scheme-code for A000203 has been given under that entry. - Antti Karttunen, Dec 02 2013

CROSSREFS

Cf. A000203, A000217, A000290, A001110.

Sequence in context: A254654 A028692 A127486 * A191946 A221639 A078398

Adjacent sequences:  A232844 A232845 A232846 * A232848 A232849 A232850

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Dec 01 2013

STATUS

approved

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Last modified June 24 20:32 EDT 2022. Contains 354830 sequences. (Running on oeis4.)