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A324723
Numbers n such that bitor(2*k, sigma(k)) == 2k, where k = A156552(n).
2
4, 8, 9, 16, 27, 30, 32, 45, 64, 72, 125, 128, 135, 144, 243, 250, 256, 270, 315, 405, 420, 480, 490, 512, 576, 600, 675, 756, 810, 825, 875, 988, 1000, 1024, 1152, 1155, 1210, 1215, 1458, 1470, 1600, 1690, 1716, 1728, 1920, 2048, 2100, 2187, 2250, 2430, 2450, 2475, 3125, 3234, 3240, 3600, 3645, 3825, 4320, 4375, 5070, 5103
OFFSET
1,1
PROG
(PARI)
A156552(n) = {my(f = factor(n), p2 = 1, res = 0); for(i = 1, #f~, p = 1 << (primepi(f[i, 1]) - 1); res += (p * p2 * (2^(f[i, 2]) - 1)); p2 <<= f[i, 2]); res}; \\ From A156552 by David A. Corneth
isA324726(n) = ((2*n)==bitor(2*n, sigma(n)));
isA324723(n) = if(n>1, isA324726(A156552(n)));
(PARI) isA324723(n) = if(1==n, 0, my(t=2*A156552(n)); (t==bitor(t, A323243(n)))); \\ Using also code from A323243.
CROSSREFS
KEYWORD
nonn
AUTHOR
Antti Karttunen, Mar 15 2019
STATUS
approved