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.

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

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