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A306510 Numbers k such that twice the number of divisors of k is equal to the number of divisors of the sum of digits of k. 0
17, 19, 37, 53, 59, 71, 73, 107, 109, 127, 149, 163, 167, 181, 233, 239, 251, 257, 271, 293, 307, 347, 383, 419, 431, 433, 491, 499, 503, 509, 521, 523, 541, 563, 613, 617, 631, 653, 699, 701, 743, 761, 769, 787, 789, 811, 859, 877, 879, 941, 967 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..51.

FORMULA

2*A000005(k) = A000005(A007953(k)).

EXAMPLE

For k = 19, 2*A000005(19) = A000005(A007953(19)), 2*A000005(19) = A000005(10), thus k = 19 is a member of the sequence.

PROG

(PARI) isok(k) = (k >= 1) && (2*numdiv(k) == numdiv(sumdigits(k, 10))); \\ Daniel Suteu, Feb 20 2019

CROSSREFS

Cf. A000005, A007953, A306509.

Sequence in context: A289355 A144214 A191043 * A129805 A289492 A262286

Adjacent sequences:  A306507 A306508 A306509 * A306511 A306512 A306513

KEYWORD

nonn,base

AUTHOR

Ctibor O. Zizka, Feb 20 2019

STATUS

approved

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Last modified February 18 12:10 EST 2020. Contains 332018 sequences. (Running on oeis4.)