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A255335 Numbers n for which there exists k < n such that A000203(k) = A000203(n) and A007947(k) = A007947(n), where A000203 gives the sum of divisors, and A007947 gives the squarefree kernel of n. 4
2058, 10290, 22638, 26754, 34986, 39102, 47334, 51450, 52728, 59682, 63798, 76146, 84378, 88494, 96726, 109074, 113190, 121422, 125538, 133770, 137886, 146118, 150234, 162582, 170814, 174930, 183162, 195510, 199626, 207858, 211974, 220206, 224322, 232554, 236670, 249018, 257250, 261366, 263640, 269598, 281946, 286062, 294294 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence A255423 sorted into ascending order.

Note that both for u = a(17) = 113190 and v = a(22) = 146118, A000203(u) = A000203(v) = 345600.

Also, both for w = a(20) = 133770 and x = a(25) = 170814, A000203(w) = A000203(x) = 403200.

Question: Does this have any common terms with A255334 ?

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..2434

PROG

(PARI)

allocatemem(234567890);

A007947(n) = factorback(factorint(n)[, 1]); \\ Andrew Lelechenko, May 09 2014

upto = (2^24)-4;

bigvec = vector(upto);

i=0; for(n=1, upto, bigvec[n] = Set([]); my(r=A007947(n), s=sigma(n)); if(setsearch(bigvec[r], s), i++; write("b255335.txt", i, " ", n), bigvec[r] = setunion(Set([s]), bigvec[r])));

(Scheme, with Antti Karttunen's IntSeq-library. Quite naive implementation.)

(define A255335 (MATCHING-POS 1 1 isA255335?))

(define (isA255335? n) (let ((sig_n (A000203 n)) (rad_n (A007947 n))) (let loop ((try (- n rad_n))) (cond ((< try rad_n) #f) ((and (= sig_n (A000203 try)) (= rad_n (A007947 try))) #t) (else (loop (- try rad_n)))))))

CROSSREFS

Subsequence of A013929.

Cf. A000203, A007947.

Cf. also A255334, A255423, A254035.

Sequence in context: A074996 A252112 A045055 * A255423 A202418 A069427

Adjacent sequences:  A255332 A255333 A255334 * A255336 A255337 A255338

KEYWORD

nonn

AUTHOR

Antti Karttunen, Mar 23 2015, suggested by Michel Marcus, Feb 23 2015

STATUS

approved

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Last modified August 18 04:50 EDT 2019. Contains 326072 sequences. (Running on oeis4.)